Question

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

• A. $1\text{m}$
• B. $2\text{m}$
• C. $3\text{m}$
• D. None of these

Answer 1

The correct option is B $2\text{m}$

The acceleration of centre of mass is
$a_{CM}=\frac{F}{m_A+m_B}=\frac{30}{10+20}=1{\text{m/s}}^2$
Distance covered by COM, $s=\frac{1}{2}{a}_{CM}{t}^2$
$⟹s=\frac{1}{2}\times 1\times 2^2=2\text{m}$