Question

A block of mass $M$ is 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 energy of the block increases by $20J$ in $1s$.

• 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 $20J$ in $1s$.
• D. The work done by the force of gravity is $20J$ in $1s$.

Answer 1

The correct option is B The tension in the string is $F$.

tension in string is equal to $F$. since pulley is light and smooth so it is only force on string resulting in tension.
work done by tension $=$ increase in K.E. $+$ increase in potential energy and work done by gravity $=$ -ve of increase in potential energy