Question

A stationary object is released from a point P at a
distance 3R from the centre of the moon which has
radius R and mass M. Which of the following gives
the speed of the object on hitting the moon?
Moon
3R​

Answer 1

Answer:

V=$\sqrt$4GM/3R  

Explanation:

Let the mass of object be mm and velocity with which it hits the moon be v.

Using conservation of energy at the point P and surface of moon :

P.EP​ + K.EP ​= P.E surface ​+ K.E surface​

∴ -GMm/3R+0=-GMm/R+1/2mv2

or

1/2mv2=2/3GMm/R

V=$\sqrt$4GM/3R