Question

Two blocks $A$ and $B$ are connected by a massless string (shown in the figure). A force of $30 \, N$ is applied on block $B$ . The distance travelled by centre of mass in $2 \, s$ starting from rest is

• A. $1m$
• B. $2m$
• C. $3m$
• D. $4m$

Answer 1

Answer: (B)

The acceleration of the centre of mass is
$a_{C M}=\frac{F}{m_{A} + m_{B}}$
$=\frac{30}{10 + 20}=1 \, m \, s^{- 2}$
$\therefore \, s=\frac{1}{2}a_{cm}t^{2}=\frac{1}{2}\times 1\times 2^{2}=2 \, m$