PHYSICS · Multi-part · AP · Physics 1: Algebra-based · Force and Translational Dynamics · Force and Translational Dynamics
Problem
Two blocks, X and Y, of unequal mass are in direct contact on a horizontal surface that can be considered friction-free for the time interval of interest. A student pushes only on block X with a constant horizontal force so that both blocks accelerate together.
Answer the following questions about the interaction between the two blocks. Assume the +x-direction is the direction of the push.
(a) Draw separate free-body diagrams for block X and for block Y. Label each force with its type (gravitational, normal, etc.) and the object exerting it.
(b) Identify every third-law action-reaction pair that involves one of the two blocks. For each pair, state the two objects involved and describe how the forces are related.
(c) Treating the two blocks as a single system, explain why the normal force that the blocks exert on each other does not influence the acceleration calculated for the system as a whole.
(d) Suppose block X has half the mass of block Y. Qualitatively compare the magnitudes of the net force acting on each individual block and explain how that comparison is consistent with the fact that the two blocks share the same acceleration.