Q : A body moving at 2m/s can be stopped over a distance x. If its kinetic energy is doubled, how long will it go before coming to rest, if the retarding force remains unchanged

(A) x

(B) 2x

(C) 4x

(D) 8x

Solution : If R = Retarding force

Rx_{1} = ΔK.E_{1} = K … (i)

Rx_{2} = ΔKE_{2} = 2K . . .(ii)

Dividing (ii) by (i)

x_{2} = 2x_{1}

= 2x