Two blocks, each of mass
m, are stacked on a horizontal floor. The static and kinetic coefficients of friction are
μs and
μk (with
μs>μk) at
both the block-block interface and the bottom-block-floor interface. Both blocks are initially at rest. A constant horizontal force
F is applied to the bottom block. Which of the following best describes the
bottom block's acceleration as a function of
F, as
F is increased from zero?