Question

Block A is placed on block B, whose mass is greater than that of the A. There is friction between the blocks, while the ground is smooth. A horizontal force P, increasing linearly with time, begins to act on A. The accelerations $a_1$ and $a_2$ of A and B respectively are plotted against time (t). Choose the correct graph.

• A.
• B.
• C.
• D.

Answer 1

The correct option is C

The two blocks will move together with the same acceleration as long as the force of friction between them is less than the limiting friction, as the only force on the lower block B is the force of friction. Once limiting friction is reached, the acceleration of B becomes constant $=\left(\frac{F_{lim}}{\text{mass of B}}\right)$, and the acceleration of A continues to increase at a faster rate.