Question

The two bodies (particles) are moving under their mutual gravitational interaction (assume no other force is acting on them), then the total work done on the two bodies in a particular time interval

• A. is always zero
• B. is always positive
• C. is always negative
• D. can be zero sometimes

Answer 1

The correct option is B

is always positive

Gravitational force:

1. The gravitational force F between two bodies of masses $m_1$and $m_2$ separated by a distance $r$ is given by,
2. $F=\frac{G{m}_1{m}_2}{r^2}$

Work:

1. By definition, work done$W=F.S=mgS$, where m is the mass of the body, F is the applied force F, S is displacement S and g is the acceleration due to gravity.
2. We know that all the quantities mentioned above are positive, thus work is also positive.
3. As there are no external forces acting on the system, the total energy of the system remains constant.

Hence option B is correct, the total work done on the two bodies in a particular interval time is always positive.