A small block rests on top of a larger block that is pulled horizontally to the right
PHYSICS · Single correct · AP · Physics 1: Algebra-based · Force and Translational Dynamics · Force and Translational Dynamics
Problem
A small block rests on top of a larger block that is pulled horizontally to the right. When the horizontal acceleration of the larger block satisfies a<μsg, the upper block does not slide. Which of the following best explains why the upper block remains at rest relative to the lower block in this situation?
(a) The inertia of the upper block balances the applied pull, so the block experiences no net horizontal force and stays fixed relative to the lower block.
(b) Static friction provides whatever horizontal force is necessary (up to a maximum of μsN) to make the upper block share the lower block's acceleration.
(c) Static friction cannot act because there is no relative motion, so no horizontal force accelerates the upper block.
(d) Kinetic friction between the two blocks is too small to overcome their combined inertia, so no relative motion occurs.