5) Three blocks, A, B and C, are lined up in that order on a smooth horizontal s
ID: 1369118 • Letter: 5
Question
5) Three blocks, A, B and C, are lined up in that order on a smooth horizontal surface and have masses 11 kg, 27 kg and 34 kg respectively. Blocks A and C are in contact with block B. You push block A towards block C with a constant horizontal force of 20 N. In the first answer box enter the magnitude of normal force that A exerts on B. In the second answer box enter the magnitude of normal force that B exerts on C.
Answer 1 of 2:
Answer 2 of 2:
6) After a hard day's work, you return home and decide to clean your apartment. In order to do so, you need to move your bed which has a mass of 100 kg. You exert a horizontal force of 300 N and your bed refuses to move. You roll up your sleeves and keep pushing until you exert a horizontal force 600 N. The bed slides a little but now you are exhausted and stop pushing. You have an aha! moment as you recall what you learned in Physics 101. Consequently, you remove the bed's mattress (37 kg) and push the bed again with the same horizontal force as before. This time the bed slides with an acceleration of 4.12 m/s^2. In the first answer box, enter the co-efficient of static friction between the bed and the floor. In the second answer box, enter the co-efficient of kinetic friction between the bed and the floor.
Answer 1 of 2:
Answer 2 of 2:
7) A ladder rests against a smooth vertical wall. The magnitudes of the normal forces from the wall and floor on the ladder are 38 N and 68 N respectively. In the first answer box enter the mass of the ladder and in the second answer box enter the magnitude of static friction force from the floor on the ladder.
Answer 1 of 2:
Answer 2 of 2:
Explanation / Answer
5) Three blocks, A, B and C, are lined up in that order on a smooth horizontal surface and have masses 11 kg, 27 kg and 34 kg respectively. Blocks A and C are in contact with block B. You push block A towards block C with a constant horizontal force of 20 N. In the first answer box enter the magnitude of normal force that A exerts on B. In the second answer box enter the magnitude of normal force that B exerts on C.
Answer 1 of 2:
Answer 2 of 2:
Total force = 20N
The total mass of the system = ma + mb +mc = 11 + 27 + 34 = 72 kg
F = Ma
20 = 72 x a
Acceleration a = 20/72 = 0.278 m/s2
The force required to accelerate block A = maa = 11 x 0.278 = 3.06 N
Of the applied 20 N the F’ is used up to move a and the block A. The remaining will be applied to block B which is Fa = 20 - 3.06 = 16.94 N
The force required to move block B = mba = 27 x 0.278 = 7.506
This force is substracted from the applied force by block A and the remaining will be given to block C
Fb = 16.94 – 7.506 = 9.434 N
6) After a hard day's work, you return home and decide to clean your apartment. In order to do so, you need to move your bed which has a mass of 100 kg. You exert a horizontal force of 300 N and your bed refuses to move. You roll up your sleeves and keep pushing until you exert a horizontal force 600 N. The bed slides a little but now you are exhausted and stop pushing. You have an aha! moment as you recall what you learned in Physics 101. Consequently, you remove the bed's mattress (37 kg) and push the bed again with the same horizontal force as before. This time the bed slides with an acceleration of 4.12 m/s^2. In the first answer box, enter the co-efficient of static friction between the bed and the floor. In the second answer box, enter the co-efficient of kinetic friction between the bed and the floor.
Answer 1 of 2:
Maximum force needed to move the bed alightly is F = 600 N
600N = µsMg
µs = 600 / (100 x 9.8) = 0.612 no unit
Answer 2 of 2:
Total force = ma + µkmg
600 = (100-37)4.12 + µk(100-37)9.8
340.44 = 617.4µk
µk = 0.551 no unit
7) A ladder rests against a smooth vertical wall. The magnitudes of the normal forces from the wall and floor on the ladder are 38 N and 68 N respectively. In the first answer box enter the mass of the ladder and in the second answer box enter the magnitude of static friction force from the floor on the ladder.
Normal force by floor on ladder 68 = mg
M = 68 / 9.8 = 6.94 kg
For the ladder to be in equilibrium the frictional force provided by floor should be equal to the normal force provided by wall = 38 N
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