Question

A metallic wire of length $L$ metre extends by $\ell$ metre when stretched by suspending a weight $Mg$ from it. The mechanical energy stored in the wire is

• A. $2Mg\ell$
• B. $Mg\ell$
• C. $\frac{Mg\ell }{2}$
• D. $\frac{Mg\ell }{4}$

Answer 1

The correct option is C $\frac{Mg\ell }{2}$

Weight Mg moves the centre of gravity of the spring through a distance $\frac{(0+\ell )}{2}=\ell /2$
$\therefore Mechanicalenergystored=Workdone=Mg\ell /2$.