A block of mass M hanging over a smooth and light pulley through a light string. The other end of the string is pulled by a constant force F. The kinetic of the block increases by `40J` in `1s`. State whether the following statements are true or false.
(a) The tension in the string is `Mg` .
(b) The work done the tension on the block is `40J`.
(c) the tension in the string is `F`.
(d) The work done by the force of gravity is 40J in the above 1s .

Options

A. The tension in the string is Mg
B. The tension in the string is F
C. The work done by the tension on the block is 20 J in the above 1s
D. The work done by the force of gravity is -20 J in the above 1s

Answer

B

Explanation

Work done by tension in the string + work done by force of gravity is equal to change in kinetic energy of the block. As the velocity is changing, so F = tension in the string is not equal to mg.