Question

The system shown is figure is released from rest. String is massless and pulley is smooth. The work done by gravity on 4 kg block in 2 s.

• A. $120J$
• B. $240J$
• C. $360J$
• D. $480J$

Answer 1

The correct option is D $480J$

Acceleration of each block= $a=\frac{m_2-m_1}{m_2+m_1}g$

$=\frac{4-1}{4+1}g=\frac{3}{5}g$

Thus the distance covered by block in 2 s, S =$\frac{1}{2}a{t}^2=\frac{1}{2}\times \frac{3}{5}g\times 2^2=12m$

Work done by gravity on 4 kg block during this time=$m_{2}gS$

$=4\times 10\times 12=480J$