Question

The force that causes the acceleration of m2 is not the applied external force; rather, it is the contact force from m1. Applying Newton's second law to m2, what is the magnitude of the contact force, P12, between the two blocks for the case above?

a) P12 is equal to the applied external force.

b) P12 is greater than the applied external force.

c) P12 is less than the applied external force.

d) P12 is equal to the gravitational force on m2.

Answer 1

The magnitude of the contact force P12 on m2 is less than the applied external force, as per Newton's third and second laws.

Step-by-step explanation:

According to Newton's third law, for every action, there is an equal and opposite reaction. This means that the force F21 (the force on m1 from m2) is equal in magnitude but opposite in direction to the force F12 (the force on m2 from m1). Applying Newton's second law, the net external force on an object is equal to the mass of the object times its acceleration (Fnet = m*a). Since m2 is only being pushed by the contact force from m1, not the external force directly, the contact force P12 on m2 is less than the total applied external force, which must accelerate both m1 and m2 combined. Thus, the correct answer is (c) P12 is less than the applied external force.