A body is displaced from position A to position B. Kinetic and potential energies of the body at positions A and B are
`K_(A)=50J, U_(A)=-30J, K_(B)=-10J` and `U_(B)=20J`.
Find work done by
(a) conservative forces (b) all forces (c)forces other than covservative forces.

Answer

D

Explanation

(a) `W_(c)=-DeltaU=-(U_(f)-U_(i))`
`=U_(i)-U_(f)=U_(A)-U_(B)`
`=-30-20=-50J`
(b) `W_(all)=DeltaK=K_(f)-K_(i)`
`=K_(B)-K_(A)`
`=10-50=-40J`
(c) Work done by the forces other than conservative
`=DeltaE_(f)-E_(i)`
`=(K_(f)+U_(f))-(K_(i)+U_(i))`
`=(K_(B)+U_(B))-(K_(A)+U_(A))`
`=(10+20)-(50-30)=10J`.