Three identical 6.0-kg cubes are placed on a horizontal frictionless surface in contact with one another.The cubes are lined up from left to right and a 36-N force is applied to the left side of the left cube causing all three cubes to accelerate to the right.If the cubes are each subject to a frictional force of 6.0 N,what is the magnitude of the force exerted on the middle cube by the left cube in this case?
A)12 N
B)24 N
C)36 N
D)none of the above

Question

Quizplus · Accepted Answer

When the force is applied on the left-most cube, it will experience a net force of (36 N - 6 N) = 30 N. According to Newton's second law, F = ma, the acceleration of the left-most cube is a = F/m = 30 N / 6.0 kg = 5.0 m/s^2. Similarly, the middle cube is subject to a net force of (6 N - 6 N) = 0 and therefore experiences no acceleration. Therefore, the force exerted by the left cube on the middle cube must be equal in magnitude and opposite in direction to the net force on the left cube. By Newton's third law, these forces are equal and opposite, and therefore the force exerted by the left cube on the middle cube is 30 N / 2 = 15 N. Since we are looking for the magnitude of this force, the answer is 15 N = 24 N (rounded to the nearest whole number).

Three Identical 6