When a ball m is thrown upwards to a height h, the work done by the force of gravity is:

1. mgh
2. -mgh
3. mg
4. mgh²

Identify the incorrect statement :

No work is done by a force F on an object if :

1. the object is stationary but the point of application of force moves on the object.
2. the object moves in such a way that the point of application of force remains fixed.
3. the force is always perpendicular to velocity.
4. the force is always perpendicular to acceleration.

A coolie A takes 1 minute to lift a load to the roof of a bus whereas coolie B take 2 minutes to lift the same load to the roof of the same bus. The work done by B is:

1. equal to work done by A
2. greater than work done by A
3. less than work done by A
4. none of the above.

The energy of electron is 2.5 eV. When expressed in Joule, it is

1. 1.6 x 10^-19 J
2. 4.0 x 10^-19 J
3. 3.2 x 10^-19 J
4. 0