The system shown remains at rest. The force of friction on the upper block is:
A) 4 N
B) 8 N
C) 12 N
D) 16 N
E) 20 N

Question

The system shown remains at rest. The force of friction on the upper block is: 
A) 4 N 
B) 8 N 
C) 12 N 
D) 16 N 
E) 20 N

Quizplus · Accepted Answer

Since the system is at rest, the net force acting on each object should be zero. Thus, the force of friction on the upper block (which is the only external force acting on the system) should be equal and opposite to the force applied on it by the lower block. This force is given by the product of the mass of the lower block and the acceleration due to gravity, which is (2 kg) * (9.8 m/s^2) = 19.6 N. Therefore, the force of friction on the upper block should also be 19.6 N, which is closest to option B (8 N) compared to the other options.

The System Shown Remains at Rest