Three blocks, each of mass 10 kg are on a frictionless table. A hand pushes on t

Question

Three blocks, each of mass 10 kg are on a frictionless table. A hand pushes on the left most box (A) such that the three boxes accelerate in the positive horizontal direction as shown at a rate of a = 0.8 m/s2.

1) What is the magnitude of the force on block A from the hand?_________ N

2) What is the net horizontal force on block A ?___________ N

3) What is the horizontal force on block A due to block B?____________ N 4)

What is the net horizontal force on block B? ___________N

5) What is the horizontal force on block B due to block C?_____________ N

Explanation / Answer

Taking all the blocks together as a system the only external force is that of the hand.Applying Newton's second law gives :

m*a=Fhand    , (3*10)*0.8=Fhand

1. The force on block A by hand is 24 N.

According to the Newton's second law the sum of all forces on any block is equal to its mass times its acceleration.Thus the net force on block A is equal to its mass times its acceleration : 10*0.8 = 8 N

2. Thus the net force on block A is 8 N.

The external forces on block A are that of the hand and that due to block B.

m*a = Fhand -Fb    , 8 = 24 - Fb   , Fb = 16 N

3. The horizontal force on block A due to block B is 16 N.

Similar to block A ,the net force on block A is equal to its mass times its acceleration : 10*0.8 = 8 N

4. Thus the net force on block B is 8 N.

The external forces on block B are that due to block A and that due to block C.

m*a = Fa -Fc    , from Newton's third law the force on block B due to block A is equal and opposite to the force on block A due to block B

8 = 16 - Fc , Fc = 8 N

5. The horizontal force on block B due to block C is 8 N.

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