Question

Two objects of massses m and 4 m are at rest at infinite separtion they move twoards each other under mutula gravitonal attraction then at a separation r which of the following is true ?
A. the total energy of the system is not zero
B. the force between them is not zero
C. the centre of mass of the system is at rest
D. all the above are true

Answer 1

Correct Answer - D
When they are at infinite distance their PE =0 and KE -0 and gravitational force `F=(Gm_(1)m_(2))/(d^(2))` is also zero when the distance of separation between the two masses becomes r
their total energy is finite
(ii) force of attraction between them is finite and
(iii) the control of mass of the system is at rest because initially the masses are at rest and there is no external force acting on the system