Question

A bar magnet is released into a copper tube. Mass of the magnet is $m$. After some time it gains a constant speed of $v_0$, then heat developed per second in conducting cylinder will be,

• A. $mg{v}_0$
• B. $\frac{3}{2}mg{v}_0$
• C. $\frac{mg{v}_0}{2}$
• D. zero

Answer 1

The correct option is A $mg{v}_0$

After gaining a constant speed,
Rate of loss of $P.E.$ = heat developed per second
$\Rightarrow \frac{d}{dt}\left(mgh\right)$ = rate of heat
$mg{v}_0$ = rate of heat