(b) The work done in pulling the string is stored as potential energy in the spring
[image:6_image109.jpeg]$\ $
$U = \frac{1}{2}kx^{2}$ ...(i)
Where k is spring constant and $x$is distance through which it is pulled.
Also in SHM
Force$\ \propto \ $displacement
$F = kx$ .......(ii)
Putting $x = \frac{F}{k}$in Eq. (i),we get
U$= \frac{1}{2}k\left( \frac{F}{k} \right)^{2} = \frac{F^{2}}{2k}$
$\therefore\frac{U_{1}}{U_{2}} = \frac{K_{2}}{K_{1}} = \frac{3000}{1500} = \frac{2}{1}$
$\therefore\ U_{1}:U_{2} = 2:1\ $