Question

Block $A$ is placed on block $B$, whose mass is greater than that of $A$. 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 B

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 value.
$a_c=\frac{P}{\text{mass of A+B}}$
After limiting friction is reached, the acceleration of B becomes constant $a_2=\frac{f_l}{\text{mass of B}}$
Acceleration of A continues to increase linearly.
$a_1=\frac{P-f_l}{\text{mass of A}}$