/*Start of Problem*/ /*Problem Num*/Problem #1 /*Difficulty*/1 /*Picture URL*/4.0a.svg /*FBD URL*/FBD1.svg /*Description*/A hand is throwing a block straight up into the sky. /*Object List*/ E=Earth, B=Block, H=Hand /*Contact Forces*/ /*Systems*/ /*Strings*/ /*Springs and spring status*/ /*FBD List*/B /*Relative Motions*/ /*Frictionless Surfaces*/ /*Accelerations*/B up /*Summary*/ /*End of Problem*/ /*Start of Problem*/ /*Problem Num*/Problem #2 /*Difficulty*/1 /*Picture URL*/4.0b.svg /*FBD URL*/FBD1.svg /*Description*/Shortly after being thrown, the block is moving straight upward.

This problem is identical to problem #1 except this problem involves the block shortly after it has been thrown. Notice the 'Copy Answers from Previous Problem' button that allows you to copy the forces from your previous answer if you choose. In addition, be aware that you can use the 'Next Problem' and 'Previous Problem' buttons to look at your previous answers if that would be helpful. /*Object List*/ E=Earth, B=Block, H=Hand /*Contact Forces*/ /*Systems*/ /*Strings*/ /*Springs and spring status*/ /*FBD List*/B /*Relative Motions*/ /*Frictionless Surfaces*/ /*Accelerations*/B down /*Paired With Previous Problem*/-1 /*Summary*/The last problem and this problem concern the same objects at two different instants in time. When the hand is touching the block, the freebody diagram includes a normal force by the hand on the block. The instant the hand breaks contact with the block, however, the normal force is gone. The moral is that whenever you draw a freebody diagram, you must draw it for a particular instant in time. /*End of Problem*/ /*Start of Problem*/ /*Problem Num*/Problem #3 /*Difficulty*/1 /*Picture URL*/4.0c.svg /*FBD URL*/FBD1.svg /*Description*/After being thrown, the block reaches its highest point.

This problem is identical to problem #1 except this problem involves the block after it reaches its highest point. Notice the 'Copy Answers from Previous Problem' button that allows you to copy the forces from your previous answer if you choose. In addition, be aware that you can use the 'Next Problem' and 'Previous Problem' buttons to look at your previous answers if that would be helpful. /*Object List*/ E=Earth, B=Block, H=Hand /*Contact Forces*/ /*Systems*/ /*Strings*/ /*Springs and spring status*/ /*FBD List*/B /*Relative Motions*/ /*Frictionless Surfaces*/ /*Accelerations*/B down /*Paired With Previous Problem*/-2 /*Summary*/Like the last problem, the block in this problem is not touching anything. Hence the only force on it is the noncontact weight force. /*End of Problem*/ /*Start of Problem*/ /*Problem Num*/Problem #4 /*Difficulty*/1 /*Picture URL*/4.0d.svg /*FBD URL*/FBD1.svg /*Description*/After being thrown upward and turning around, a block is now falling straight down.

This problem is identical to problem #1 except this problem involves the block after it is falling back down. Notice the 'Copy Answers from Previous Problem' button that allows you to copy the forces from your previous answer if you choose. In addition, be aware that you can use the 'Next Problem' and 'Previous Problem' buttons to look at your previous answers if that would be helpful. /*Object List*/ E=Earth, B=Block, H=Hand /*Contact Forces*/ /*Systems*/ /*Strings*/ /*Springs and spring status*/ /*FBD List*/B /*Relative Motions*/ /*Frictionless Surfaces*/ /*Accelerations*/B down /*Paired With Previous Problem*/-3 /*Summary*/Like the last two problems, the block in this problem is not touching anything. Hence the only force on it is the noncontact weight force. Whether the block is rising, at the top of its motion or is falling makes no difference to its freebody diagram. /*End of Problem*/ /*Start of Problem*/ /*Problem Num*/Problem #5 /*Difficulty*/1 /*Picture URL*/4.1a.svg /*FBD URL*/FBD1.svg /*Description*/A hand pushes a block horizontally so that it slides to the right at constant speed. /*Object List*/ E=Earth, B=Block, H=Hand /*Contact Forces*/HB 0 horizontally /*Systems*/ /*Strings*/ /*Springs and spring status*/ /*FBD List*/B /*Relative Motions*/B right E /*Frictionless Surfaces*/ /*Accelerations*/B zero /*Summary*/Notice this freebody diagram includes two different normal forces. One definition of the word 'normal' is perpendicular. Indeed, both of the normal force on this freebody diagram are perpendicular to the surface between their 'by' and 'on' objects.

Friction forces are always parallel to the surface between the 'by' and 'on' objects. In addition, the direction of a friction force on an object always opposes the direction the object is sliding relative to the surface against which it is sliding. /*End of Problem*/ /*Start of Problem*/ /*Problem Num*/Problem #6 /*Difficulty*/1 /*Picture URL*/4.1b.svg /*FBD URL*/FBD1.svg /*Description*/Previously, the block was given a quick shove. Now it is sliding to the right.

This problem is identical to the previous problem (i.e., problm #5) except this problem involves an instant in time after the instant in that problem. Notice the 'Copy Answers from Previous Problem' button that allows you to copy the forces from your previous answer if you choose. In addition, be aware that you can use the 'Next Problem' and 'Previous Problem' buttons to look at your previous answers if that would be helpful. /*Object List*/ E=Earth, B=Block, H=Hand /*Systems*/ /*Strings*/ /*Springs and spring status*/ /*FBD List*/B /*Relative Motions*/B right E /*Frictionless Surfaces*/ /*Accelerations*/ /*Paired With Previous Problem*/-1 /*Summary*/This freebody diagram is identical to the last one, except the normal force is gone because the hand is no longer touching the block. /*End of Problem*/ /*Start of Problem*/ /*Problem Num*/Problem #7 /*Difficulty*/1 /*Picture URL*/4.1a.svg /*FBD URL*/FBD1.svg /*Description*/A hand pushes a book diagonally downward so that it moves to the right at constant speed.

This problem is identical to problem #5 except this time the hand pushes diagonally downward instead of horizontally. Notice the 'Copy Answers from Previous Problem' button that allows you to copy the forces from your previous answer if you choose. In addition, be aware that you can use the 'Next Problem' and 'Previous Problem' buttons to look at your previous answers if that would be helpful. /*Object List*/ E=Earth, B=Block, H=Hand /*Contact Forces*/HB 45 diagonally downward /*Systems*/ /*Strings*/ /*Springs and spring status*/ /*FBD List*/B /*Relative Motions*/B right E /*Frictionless Surfaces*/ /*Accelerations*/B zero /*Paired With Previous Problem*/-2 /*Summary*/A contact force that is exerted diagonally on a surface can be broken into two components, one of which is perpendicular to the surface and the other which is parallel to the surface. The component that is perpendicular to the surface the normal force. The component that is parallel to the surface is the friction force. /*End of Problem*/ /*Start of Problem*/ /*Problem Num*/Problem #8 /*Difficulty*/1 /*Picture URL*/4.1h.svg /*FBD URL*/FBD1.svg /*Description*/A hand pushes a book diagonally downward so that it moves to the right at constant speed.

This problem is similar to problem #7, except this time the hand touches the top of the block instead of on its side. Notice the 'Copy Answers from Previous Problem' button that allows you to copy the forces from problem #1 if you choose. In addition, be aware that you can use the 'Next Problem' and 'Previous Problem' buttons to look at your previous answers if that would be helpful. /*Object List*/ E=Earth, B=Block, H=Hand /*Contact Forces*/HB 45 diagonally downward /*Systems*/ /*Strings*/ /*Springs and spring status*/ /*FBD List*/B /*Relative Motions*/B right E /*Frictionless Surfaces*/ /*Accelerations*/B zero /*Paired With Previous Problem*/-1 /*Summary*/ /*End of Problem*/ /*Start of Problem*/ /*Problem Num*/Problem #9 /*Difficulty*/1 /*Picture URL*/4.1c.svg /*FBD URL*/FBD1.svg /*Description*/The block is being pulled so that it slides at constant speed to the right.

This problem is yet another that is identical to problem #5 except this time the block is being pulled rather than being pushed. Notice the 'Copy Answers from Previous Problem' button that allows you to copy the forces from your previous answer if you choose. In addition, be aware that you can use the 'Next Problem' and 'Previous Problem' buttons to look at your previous answers if that would be helpful. /*Object List*/ E=Earth, B=Block, H=Hand, S=String /*Systems*/ /*Strings*/S /*Springs and spring status*/ /*FBD List*/B /*Relative Motions*/B right E /*Frictionless Surfaces*/ /*Accelerations*/B zero /*Paired With Previous Problem*/-4 /*Summary*/A push is a normal force. A pull is a tension force.

Tension forces caused by a string are always parallel to the string. /*End of Problem*/ /*Start of Problem*/ /*Problem Num*/Problem #10 /*Difficulty*/1 /*Picture URL*/4.1c.svg /*FBD URL*/FBD1.svg /*Description*/The block is being pulled, but not hard enough to make it move.

This problem is identical to the previous problem (i.e., problem #9) except this time the block is not pulled hard enough to make it begin to slide. Notice the 'Copy Answers from Previous Problem' button that allows you to copy the forces from your previous answer if you choose. In addition, be aware that you can use the 'Next Problem' and 'Previous Problem' buttons to look at your previous answers if that would be helpful. /*Object List*/ E=Earth, B=Block, H=Hand, S=String /*Systems*/ /*Strings*/S /*Springs and spring status*/ /*FBD List*/B /*Relative Motions*/B zero E /*Frictionless Surfaces*/ /*Accelerations*/B zero /*Paired With Previous Problem*/-1 /*Summary*/The block in this problem is not moving. Put in other words, it is in static equilibrium. The net force on any object in static equilibrium is zero. Hence if the block in this problem is being pulled to the right, then there must be a second force on the block to the left so that the total is zero. That second force is a friction force.

This type of friction is called static friction. The type of friction exerted on a block that is sliding is called kinetic friction. Even though there are two different types of friction, this simulation uses the same symbol (f) to represent both. /*End of Problem*/ /*Start of Problem*/ /*Problem Num*/Problem #11 /*Difficulty*/1 /*Picture URL*/4.2i.svg /*FBD URL*/FBD1.svg /*Description*/The block has a hook, and the hand pulls the hook horizontally so that the block slides to the right at constant speed.

This problem is identical to the problem #9, except this time the block is pulled by a hook instead of a string. Notice the 'Copy Answers from Previous Problem' button that allows you to copy the forces from your previous answer if you choose. In addition, be aware that you can use the 'Next Problem' and 'Previous Problem' buttons to look at your previous answers if that would be helpful. /*Object List*/ E=Earth, B=Block, H=Hand, S=String /*Systems*/ /*Strings*/ /*Springs and spring status*/ /*FBD List*/B /*Relative Motions*/B right E /*Frictionless Surfaces*/ /*Accelerations*/B zero /*Paired With Previous Problem*/-2 /*Summary*/One could argue that instead of 'pulling' the block, the hand is 'pushing' the block's hook. For problems such as this one, the distinction between a 'push' and a 'pull' is a somewhat arbitrary. This simulation uses the convention that a push on an object (i.e., a normal force) points inward towards the center of mass of the object. A pull (i.e., a tension force) points outward away from the center of mass of the object. /*End of Problem*/ /*Start of Problem*/ /*Problem Num*/Problem #12 /*Difficulty*/1 /*Picture URL*/4.1g.svg /*FBD URL*/FBD1.svg /*Description*/The block is being pushed at constant speed up an incline. Assume the hand pushes at the same angle as the incline.

This problem is similar to problem #5, except this time the block is pushed up an incline instead of across a flat surface. Notice the 'Copy Answers from Previous Problem' button that allows you to copy the forces from problem #1 if you choose. In addition, be aware that you can use the 'Next Problem' and 'Previous Problem' buttons to look at your previous answers if that would be helpful. /*Object List*/ E=Earth, B=Block, H=Hand /*Contact Forces*/HB -30 at the same angle as the incline /*Systems*/ /*Strings*/ /*Springs and spring status*/ /*FBD List*/B /*Relative Motions*/B up E /*Frictionless Surfaces*/ /*Accelerations*/B zero /*Paired With Previous Problem*/-7 /*Summary*/Notice that the normal and friction forces by the inclined earth on the block are both diagonal. The normal force on the block is perpendicular to the side of the block touching the earth and the friction is parallel to that side. /*End of Problem*/ /*Start of Problem*/ /*Problem Num*/Problem #13 /*Difficulty*/1 /*Picture URL*/4.1g.svg /*FBD URL*/FBD1.svg /*Description*/The block is being pushed at constant speed up an incline. Assume the hand pushes horizontally.

This problem is similar to problem #11, except this time the hand pushes horizontally instead of pushing at the same angle as the incline. Notice the 'Copy Answers from Previous Problem' button that allows you to copy the forces from problem #1 if you choose. In addition, be aware that you can use the 'Next Problem' and 'Previous Problem' buttons to look at your previous answers if that would be helpful. /*Object List*/ E=Earth, B=Block, H=Hand /*Contact Forces*/HB 0 horizontally /*Systems*/ /*Strings*/ /*Springs and spring status*/ /*FBD List*/B /*Relative Motions*/B up E /*Frictionless Surfaces*/ /*Accelerations*/B zero /*Paired With Previous Problem*/-1 /*Summary*/Notice that both normal forces on the freebody diagram of the block are perpendicular to the surface on which the forces act. In addition, both friction forces are parallel to the surfaces of the block on which the friction forces act. /*End of Problem*/ /*Start of Problem*/ /*Problem Num*/Problem #14 /*Difficulty*/1 /*Picture URL*/4.1e.svg /*FBD URL*/FBD1.svg /*Description*/The block is attached to a stretched spring. /*Object List*/ E=Earth, B=Block, S=Spring, C=Ceiling /*Systems*/ /*Strings*/ /*Springs and spring status*/S stretched /*FBD List*/B /*Relative Motions*/ /*Frictionless Surfaces*/ /*Accelerations*/ /*Summary*/This problem involves a stretched spring. A stretched spring is one that is longer than it is when it is relaxed. Stretched springs 'pull'. Since the spring in the problem is touching the top of the block, it is pulling the top of the block upward. /*End of Problem*/ /*Start of Problem*/ /*Problem Num*/Problem #15 /*Difficulty*/1 /*Picture URL*/4.1e.svg /*FBD URL*/FBD1.svg /*Description*/The block is attached to a compressed spring.

This problem is identical to the previous problem (i.e., problem #14) except this time the spring is compressed instead of stretched. Notice the 'Copy Answers from Previous Problem' button that allows you to copy the forces from your previous answer if you choose. In addition, be aware that you can use the 'Next Problem' and 'Previous Problem' buttons to look at your previous answers if that would be helpful. /*Object List*/ E=Earth, B=Block, S=Spring, C=Ceiling /*Systems*/ /*Strings*/ /*Springs and spring status*/S compressed /*FBD List*/B /*Relative Motions*/ /*Frictionless Surfaces*/ /*Accelerations*/ /*Paired With Previous Problem*/-1 /*Summary*/This problem involves a compressed spring. A compressed spring is one that is shorter than it is when it is relaxed. Compressed springs 'push'. Since the spring in this problem is touching the top of the block, it is pushing the top of the block downward.

Be aware that nothing in this problem states that this block must be in static equilibrium. In fact, if the spring really is compressed, the the block is not in static equilibrium. Both the spring and gravity are pushing it downward. /*End of Problem*/ /*Start of Problem*/ /*Problem Num*/Problem #16 /*Difficulty*/2 /*Picture URL*/4.1j.svg /*FBD URL*/FBD1.svg /*Description*/The block is attached to a compressed spring and a string. The block sits at rest. /*Object List*/ E=Earth, B=Block, L=Left Wall, R=Right Wall, S=String ,P=Spring /*Systems*/ /*Strings*/S /*Springs and spring status*/P compressed /*FBD List*/B /*Relative Motions*/ /*Frictionless Surfaces*/ /*Accelerations*/B zero /*Summary*/ /*End of Problem*/ /*Start of Problem*/ /*Problem Num*/Problem #17 /*Difficulty*/2 /*Picture URL*/4.2a.svg /*FBD URL*/FBD3.svg /*Description*/One block sits on top of the other. Both blocks are at rest. /*Object List*/ E=Earth, Y=Yellow Block, B=Blue Block, S=System of Two Blocks /*Systems*/S=Y+B /*Strings*/ /*Springs and spring status*/ /*FBD List*/B, Y, S /*Relative Motions*/Y zero B, B zero E /*Frictionless Surfaces*/ /*Accelerations*/ /*Summary*/ /*End of Problem*/ /*Start of Problem*/ /*Problem Num*/Problem #18 /*Difficulty*/2 /*Picture URL*/4.2j.svg /*FBD URL*/FBD3.svg /*Description*/One block sits on top of the other. A hand pushes horizontally on the top block, but not hard enough to make the blocks move.

This problem is identical to the previous problem (i.e., problem #17) except this time the top block is being pushed. In the last problem, it was not. Notice the 'Copy Answers from Previous Problem' button that allows you to copy the forces from your previous answer if you choose. In addition, be aware that you can use the 'Next Problem' and 'Previous Problem' buttons to look at your previous answers if that would be helpful. /*Object List*/ E=Earth, Y=Yellow Block, B=Blue Block, S=System of Two Blocks, H=Hand /*Contact Forces*/HY 0 horizontally /*Systems*/S=Y+B /*Strings*/ /*Springs and spring status*/ /*FBD List*/B, Y, S /*Relative Motions*/Y zero B, B zero E /*Frictionless Surfaces*/ /*Accelerations*/B zero, Y zero /*Paired With Previous Problem*/-1 /*Summary*/ /*End of Problem*/ /*Start of Problem*/ /*Problem Num*/Problem #19 /*Difficulty*/2 /*Picture URL*/4.2b.svg /*FBD URL*/FBD3.svg /*Description*/Two blocks sit are pushed against the ceiling by a hand. Assume the hand pushes straight up. /*Object List*/ E=Earth, Y=Yellow Block, B=Blue Block, H=Hand, C=Ceiling, S=System of Two Blocks /*Contact Forces*/HY -90 straight up /*Systems*/S=Y+B /*Strings*/ /*Springs and spring status*/ /*FBD List*/B, Y, S /*Relative Motions*/Y zero B, B zero C /*Frictionless Surfaces*/ /*Accelerations*/Y zero, B zero, S zero /*Summary*/ /*End of Problem*/ /*Start of Problem*/ /*Problem Num*/Problem #20 /*Difficulty*/3 /*Picture URL*/4.2b.svg /*FBD URL*/FBD3.svg /*Description*/Two blocks sit are pushed against the ceiling by a hand. Assume the hand pushes up and to the left.

This problem is identical to the previous problem (i.e., problem #19) except this time the hand pushes up and to the left instead of straight up. Notice the 'Copy Answers from Previous Problem' button that allows you to copy the forces from your previous answer if you choose. In addition, be aware that you can use the 'Next Problem' and 'Previous Problem' buttons to look at your previous answers if that would be helpful. /*Object List*/ E=Earth, Y=Yellow Block, B=Blue Block, H=Hand, C=Ceiling, S=System of Two Blocks /*Contact Forces*/HY -135 up and to the left /*Systems*/S=Y+B /*Strings*/ /*Springs and spring status*/ /*FBD List*/B, Y, S /*Relative Motions*/Y zero B, B zero C /*Frictionless Surfaces*/ /*Accelerations*/Y zero, B zero, S zero /*Paired With Previous Problem*/-1 /*Summary*/ /*End of Problem*/ /*Start of Problem*/ /*Problem Num*/Problem #21 /*Difficulty*/2 /*Picture URL*/4.2c.svg /*FBD URL*/FBD3.svg /*Description*/Two blocks are pulled so that they slide to the left at constant speed. /*Object List*/E=Earth, Y=Yellow Block, B=Blue Block, S=String, H=Hand, 2=System of Two Blocks /*Systems*/2=Y+B /*Strings*/S /*Springs and spring status*/ /*FBD List*/B, Y, 2 /*Relative Motions*/Y left E, B left E /*Frictionless Surfaces*/ /*Accelerations*/Y zero, B zero /*Summary*/ /*End of Problem*/ /*Start of Problem*/ /*Problem Num*/Problem #22 /*Difficulty*/2 /*Picture URL*/4.2k.svg /*FBD URL*/FBD3.svg /*Description*/Two blocks are pushed so that they slide to the left at constant speed. Assume the hand pushes horizontally.

This problem is similar to the previous problem (i.e., problem #21) except this time the blocks are being pushed instead of pulled. Notice the 'Copy Answers from Previous Problem' button that allows you to copy the forces from your previous answer if you choose. In addition, be aware that you can use the 'Next Problem' and 'Previous Problem' buttons to look at your previous answers if that would be helpful. /*Object List*/E=Earth, Y=Yellow Block, B=Blue Block, H=Hand, S=System of Two Blocks /*Systems*/S=Y+B /*Contact Forces*/HY 180 horizontally to the left /*Strings*/ /*Springs and spring status*/ /*FBD List*/B, Y, S /*Relative Motions*/Y left E, B left E /*Frictionless Surfaces*/ /*Accelerations*/Y zero, B zero /*Paired With Previous Problem*/-1 /*Summary*/ /*End of Problem*/ /*Start of Problem*/ /*Problem Num*/Problem #23 /*Difficulty*/3 /*Picture URL*/4.2f.svg /*FBD URL*/FBD3.svg /*Description*/The block sits at rest on a wedge which is also stationary. /*Object List*/ E=Earth, Y=Yellow Block, B=Blue Wedge, S=Block & Wedge System /*Systems*/S=Y+B /*Strings*/ /*Springs and spring status*/ /*FBD List*/Y, B, S /*Relative Motions*/Y zero B, B zero E /*Frictionless Surfaces*/ /*Accelerations*/Y zero, B zero /*Summary*/ /*End of Problem*/ /*Start of Problem*/ /*Problem Num*/Problem #24 /*Difficulty*/3 /*Picture URL*/4.2m.svg /*FBD URL*/FBD3.svg /*Description*/The block sits at rest on a wedge which is also stationary. There is no friction between the block and wedge. The block is held at rest by a hand which pushes perpendicular to the surface of the block.

This problem is similar to the previous problem (i.e., problem #23) except this time the block is held at rest by a hand instead of by friction. Notice the 'Copy Answers from Previous Problem' button that allows you to copy the forces from your previous answer if you choose. In addition, be aware that you can use the 'Next Problem' and 'Previous Problem' buttons to look at your previous answers if that would be helpful. /*Object List*/ E=Earth, Y=Yellow Block, B=Blue Wedge, H=Hand, S=Block & Wedge System /*Contact Forces*/HY -30 perpendicular to the surface of the block /*Systems*/S=Y+B /*Strings*/ /*Springs and spring status*/ /*FBD List*/Y, B, S /*Relative Motions*/Y zero B, B zero E /*Frictionless Surfaces*/Y B /*Accelerations*/Y zero, B zero /*Paired With Previous Problem*/-1 /*Summary*/At first glance, you might think this problem is a minor variation of the previous problem. If you compare the freebody diagrams for the Yellow Block, you would be correct. The first problem includes a friction by the Blue Wedge on the Yellow Block. In the second, this force becomes a normal force by the Hand on the Yellow Block. If you compare the freebody diagrams of the Block & Wedge System, however, you will see an important difference. In the first problem, there are no horizontal forces. In the second, in addition to the force by the Hand which has a horizontal component, there is also a horizontal friction force by the Earth on the Wedge. In the first problem, the friction force by the Blue Wedge on the Yellow block is an internal force for the Block & Wedge system because the force is by an object (the Blue Wedge) that is part of the system. In the second problem, the normal force by the hand on the Yellow block is an external force for the Block & Wedge system because the Hand is not part of the system. That external force then causes a second external force on the system (the friction by the Earth on the Blue Block) so that the net force remains zero. /*End of Problem*/ /*Start of Problem*/ /*Problem Num*/Problem #25 /*Difficulty*/3 /*Picture URL*/4.2m.svg /*FBD URL*/FBD3.svg /*Description*/The block sits at rest on a wedge which is also stationary. There is no friction between the block and wedge. The block is held at rest by a hand which pushes horizontally.

This problem is similar to the previous problem (i.e., problem #24) except this time hand pushes horizontally instead of diagonally. Notice the 'Copy Answers from Previous Problem' button that allows you to copy the forces from your previous answer if you choose. In addition, be aware that you can use the 'Next Problem' and 'Previous Problem' buttons to look at your previous answers if that would be helpful. /*Object List*/ E=Earth, Y=Yellow Block, B=Blue Wedge, H=Hand, S=Block & Wedge System /*Contact Forces*/HY 0 horizontally /*Systems*/S=Y+B /*Strings*/ /*Springs and spring status*/ /*FBD List*/Y, B, S /*Relative Motions*/Y zero B, B zero E /*Frictionless Surfaces*/Y B /*Accelerations*/Y zero, B zero /*Paired With Previous Problem*/-1 /*Summary*/ /*End of Problem*/ /*Start of Problem*/ /*Problem Num*/Problem #26 /*Difficulty*/2 /*Picture URL*/4.2e.svg /*FBD URL*/FBD2.svg /*Description*/The yellow block slows down while sliding down the incline. /*Object List*/E=Earth, Y=Yellow Block, B=Blue Block, 1=First Part of String, 2=Second Part of String, P=Pulley, S=String /*Systems*/S=1+2 /*Strings*/1, 2 /*Springs and spring status*/ /*FBD List*/Y, B /*Relative Motions*/Y down E /*Frictionless Surfaces*/ /*Accelerations*/Y upright, B down /*Summary*/ /*End of Problem*/ /*Start of Problem*/ /*Problem Num*/Problem #27 /*Difficulty*/2 /*Picture URL*/4.3b.svg /*FBD URL*/FBD2.svg /*Description*/A string is wrapped around two pulleys. /*Object List*/ E=Earth, C=Ceiling, G=Green Pulley, B=Blue Pulley, 1=First Part of the String, 2=Second Part of the String, 3=Third Part of the String, H=Hand, Y=Yellow Block, R=Rope, W=Wire, S=String, A=Green Pulley & Rope & Yellow Block /*Systems*/S=1+2+3, A=G+R+Y /*Strings*/1, 2, 3, W, R /*Springs and spring status*/ /*FBD List*/A, B /*Relative Motions*/ /*Frictionless Surfaces*/ /*Accelerations*/ /*Summary*/ /*End of Problem*/ /*Start of Problem*/ /*Problem Num*/Problem #28 /*Difficulty*/3 /*Picture URL*/4.3c.svg /*FBD URL*/FBD3.svg /*Description*/Two blocks slide together to the right at constant speed when a hand pushes the top block horizontally. /*Object List*/ E=Earth, Y=Yellow Block, B=Blue Block, H=Hand, S=Two Block System /*Contact Forces*/HY 0 horizontally /*Systems*/S=Y+B /*Strings*/ /*Springs and spring status*/ /*FBD List*/Y, B, S /*Relative Motions*/Y zero B, B right E /*Frictionless Surfaces*/ /*Accelerations*/B zero /*Summary*/ /*End of Problem*/ /*Start of Problem*/ /*Problem Num*/Problem #29 /*Difficulty*/3 /*Picture URL*/4.3d.svg /*FBD URL*/FBD3.svg /*Description*/Two blocks slide together to the right at constant speed when a hand pushes the botton block horizontally.

This problem is identical to problem #28 except this time the hand pushes the bottom block instead of the top block. Notice the 'Copy Answers from Previous Problem' button that allows you to copy the forces from your previous answer if you choose. In addition, be aware that you can use the 'Next Problem' and 'Previous Problem' buttons to look at your previous answers if that would be helpful. /*Object List*/ E=Earth, Y=Yellow Block, B=Blue Block, H=Hand, S=Two Block System /*Contact Forces*/HB 0 horizontally /*Systems*/S=Y+B /*Strings*/ /*Springs and spring status*/ /*FBD List*/Y, B, S /*Relative Motions*/Y zero B, B right E /*Frictionless Surfaces*/ /*Accelerations*/Y zero, B zero /*Paired With Previous Problem*/-1 /*Summary*/ /*End of Problem*/ /*Start of Problem*/ /*Problem Num*/Problem #30 /*Difficulty*/3 /*Picture URL*/4.2g.svg /*FBD URL*/FBD3.svg /*Description*/A hand and a spring hold a block and a wedge so that they do not move. Assume that there is no friction between the Yellow Block and the Blue Wedge or between the Blue Wedge and the Earth. In addition, assume that the push by the Hand is perpendicular to the surface of the Yellow Block. /*Object List*/ E=Earth, W=Wall, Y=Yellow Block, B=Blue Wedge, H=Hand, P=Spring, S=Block & Wedge System /*Contact Forces*/HY -30 perpendicular to the surface of the Yellow Block /*Systems*/S=Y+B /*Strings*/ /*Springs and spring status*/P unknown /*FBD List*/B, Y, S /*Relative Motions*/Y zero B, B zero E /*Frictionless Surfaces*/Y B, B E /*Accelerations*/Y zero, B zero, P zero /*Summary*/ /*End of Problem*/ /*Start of Problem*/ /*Problem Num*/Problem #31 /*Difficulty*/3 /*Picture URL*/4.2h.svg /*FBD URL*/FBD3.svg /*Description*/A hand and a spring hold a block and a wedge so that they do not move. Assume that there is no friction between the Yellow Block and the Blue Wedge or between the Blue Wedge and the Earth.

This problem is identical to problem #31 except the Hand is pushing against a different side of the Yellow Block. Notice the 'Copy Answers from Previous Problem' button that allows you to copy the forces from your previous answer if you choose. In addition, be aware that you can use the 'Next Problem' and 'Previous Problem' buttons to look at your previous answers if that would be helpful. /*Object List*/ E=Earth, W=Wall, Y=Yellow Block, B=Blue Wedge, H=Hand, P=Spring, S=Block & Wedge System /*Contact Forces*/ /*Systems*/S=Y+B /*Strings*/ /*Springs and spring status*/P unknown /*FBD List*/B, Y, S /*Relative Motions*/Y zero B, B zero E /*Frictionless Surfaces*/Y B, B E /*Accelerations*/Y zero, B zero, P zero /*Paired With Previous Problem*/-1 /*Summary*/ /*End of Problem*/ /*Start of Problem*/ /*Problem Num*/Problem #32 /*Difficulty*/3 /*Picture URL*/4.3h.svg /*FBD URL*/FBD3.svg /*Description*/A hand holds two shapes so that they remain at rest. Assume the hand pushes perpendicular to the surface of the Yellow Block. /*Object List*/ E=Earth, Y=Yellow Block, B=Blue Shape, H=Hand, S=System of Two Shapes /*Contact Forces*/HY 105 perpendicular to the surface of the Yellow Block. /*Systems*/S=Y+B /*Strings*/ /*Springs and spring status*/ /*FBD List*/B, Y, S /*Relative Motions*/Y zero B, B zero E /*Frictionless Surfaces*/ /*Accelerations*/Y zero, B zero /*Summary*/ /*End of Problem*/ /*Start of Problem*/ /*Problem Num*/Problem #33 /*Difficulty*/3 /*Picture URL*/4.3i.svg /*FBD URL*/FBD3.svg /*Description*/The two shapes are at rest. /*Object List*/ E=Earth, Y=Yellow Shape, B=Blue Shape, S=System of Two Shapes /*Contact Forces*/ /*Systems*/S=Y+B /*Strings*/ /*Springs and spring status*/ /*FBD List*/B, Y, S /*Relative Motions*/Y zero B, B zero E /*Frictionless Surfaces*/ /*Accelerations*/Y zero, B zero /*Summary*/ /*End of Problem*/ /*Start of Problem*/ /*Problem Num*/Problem #34 /*Difficulty*/3 /*Picture URL*/4.3g.svg /*FBD URL*/FBD3.svg /*Description*/A hand holds two shapes so that they remain at rest. The surface between the two shapes is frictionless.

This problem is similar to the last problem, however in this problem, there is a hand and there is no friction between the two shapes. Notice the 'Copy Answers from Previous Problem' button that allows you to copy the forces from your previous answer if you choose. In addition, be aware that you can use the 'Next Problem' and 'Previous Problem' buttons to look at your previous answers if that would be helpful. /*Object List*/ E=Earth, Y=Yellow Shape, B=Blue Shape, H=Hand, S=System of Two Shapes /*Contact Forces*/ /*Systems*/S=Y+B /*Strings*/ /*Springs and spring status*/ /*FBD List*/B, Y, S /*Relative Motions*/Y zero B, B zero E /*Frictionless Surfaces*/Y B /*Accelerations*/Y zero, B zero /*Paired With Previous Problem*/-1 /*Summary*/ /*End of Problem*/ /*Start of Problem*/ /*Problem Num*/Problem #35 /*Difficulty*/3 /*Picture URL*/4.4b.svg /*FBD URL*/FBD3.svg /*Description*/Two blocks sit at rest on the earth. /*Object List*/ E=Earth, Y=Yellow Block, B=Blue Block /*Contact Forces*/ /*Systems*/ /*Strings*/ /*Springs and spring status*/ /*FBD List*/Y, B, E /*Relative Motions*/Y zero B, B zero E /*Frictionless Surfaces*/ /*Accelerations*/Y zero, B zero, E zero /*Summary*/All forces come in pairs. If object A exerts a force on object B, then object B most certainly exerts a force back on object A. Not only does this fact hold for contact forces, but it also holds for noncontact gravitational forces. If the earth gravitationally attracts a block, then the block gravitationally attracts the earth in the opposite direction.

Be aware that some instructors do not use the term 'weight' to describe the upward directed gravitational force by the block on the earth. Whether or not such a force is called 'weight', however, does not alter the fact that it forms a pair with the downward directed weight force by the earth on the block. /*End of Problem*/