If the acceleration due to gravity at the surface of earth is \(g,\) the work done in slowly lifting a body of mass \(m\) from the earth's surface to a height \(R\) equal to the radius of the earth is:
1. \(\frac 12\)\(mgR\)
2. \(2mgR\)
3. \(mgR\)
4. \(\frac 14\)\(mgR\)

A person brings a mass of 1 kg from infinity to a point A. Initially, the mass was at rest but it moves at a speed of 2 m s^–1 as it reaches A. The work done by the person on the mass is –3 J. The potential at A is:

1. –3 J/kg^–1

2. –2 J/kg^–1

3. –5 J/kg^–1

4. none of these

The magnitude of gravitational potential energy of the moon-earth system is U with zero potential energy at infinite separation. The kinetic energy of the moon with respect to the earth is K.

1. U < K

2. U > K

3. U = K

4.