Two blocks are accelerated across a horizontal frictionless surface as shown.Frictional forces keep the two blocks from sliding relative to each other,and the two move with the same acceleration.If F = 1.2 N and M = 1.0 kg,what is the horizontal component (frictional force)of the force of the large block on the small block?
A)0.40 N to the left
B)0.80 N to the right
C)0.40 N to the right
D)0.80 N to the left
E)1.20 N to the left

Question

Two blocks are accelerated across a horizontal frictionless surface as shown.Frictional forces keep the two blocks from sliding relative to each other,and the two move with the same acceleration.If F = 1.2 N and M = 1.0 kg,what is the horizontal component (frictional force)of the force of the large block on the small block? 
A)0.40 N to the left 
B)0.80 N to the right 
C)0.40 N to the right 
D)0.80 N to the left 
E)1.20 N to the left

Quizplus · Accepted Answer

Since both blocks are moving with the same acceleration, the force of friction between them must be equal in magnitude to the force exerted by the larger block on the smaller block. Using Newton's second law, F=ma, we can find the acceleration of both blocks: a=F/M=1.2 N/1.0 kg=1.2 m/s^2. Therefore, the force of friction between the blocks is Ff=ma=1.0 kg x 1.2 m/s^2=1.2 N. Since the frictional force keeps the blocks from sliding relative to each other, it must be directed to the right, opposite to the direction of the applied force. Therefore, the horizontal component of the force of the larger block on the smaller block is also to the right, equal in magnitude to the force of friction: 0.4 N (since the force is split between the two blocks, 0.8 N is the total force of the larger block on the system). The correct answer is therefore choice C.

Two Blocks Are Accelerated Across a Horizontal Frictionless Surface as Shown.Frictional