Question

A light inextensible string that goes over a smooth fixed pulley as shown in the figure connects two blocks of masses $0.36kg$ and $0.72kg$. Taking $g=10m/s^2$, find the work done (in joules) by the string on the block of mass 0.36 kg during the first second after the system is released from rest.

Answer 1

$2mg-T=\left(2m\right)a$
$T-mg=ma$
$\Rightarrow a=g/3$
$T=\frac{4mg}{3}$
$w=T\times s=T\times \frac{1}{2}a{t}^2=\frac{4mg}{3}\times \frac{1}{2}\times \frac{g}{3}\times 1^2=\frac{200}{9}\times 0.36=8Joules$