If force F is applied on a body and it moves with a velocity v, the power will be

Explanation

`m(dv)/(dt)=F-ilB`...(1)
`i=(Blv)/(R+r)` ..(2)
`m(dv)/(dt)=F-(B^(2)l^(2)v)/(R+r)`
let `K=(B^(2)l^(2))/(R+r)`
`underset(0)overset(v)int(dV)/(F-Kv)=underset(0)overset(t)int(dt)/(m)`
`-1/K[ln(F-KV)]_(0)^(v)=t/m`
`ln((F-kV)/F)=-(Kt)/m`
`F-KV=F_(e)^(-kt//m)`
`V=F/K(1-(e)^(-kt//m)`