Consider the situation of the previous problem. (a) Calculate the force needed to keep the sliding wire moving with a constant velocity v. (b) If the force needed just after t = 0 is `F_0`, find the time at which the force needed will be `F_0` /2.

Explanation

`e=Bvl`
`i=(e/R)=(Bvl)/(2r(l+vt))`
`(a) F=i//B=(Bvl)/(2r(l+vt))xxlB`
`(B^2l^2v)/(2r(l+vt))`
`(c )Just after t=0 `
`F_0=i//B=lB((lBv)/(2rl))`
`=(lB^2v)/2r`
`(F_0)/2=(lB^2v)/(4r)=(l^2B^2v)/(2r(l+vt))`
`implies2l=l+vt`
` impliest=(1/v)`.