Give reasons for the following Hammer drives a nail into the wood only when it is lifted up and then struck.
Answer
On lifting the Hammer, its potential energy is stored in the hammer on striking the nail with a hammer this energy is used in driving the nail into the wood.
Work is said to be done only when the force applied on a body makes the body move $($i.e. if there is some displacement or motion occurred due that force$)$.
A body of mass m is moved from ground to a height h. If force of gravity on mass of $1 \ kg$ is g newton, find the potential energy stored in the body.
Answer
This work done $W$ is stored in the body in the form of Potential energy $P. E. = mgh.$
It takes $20\ s$ for a girl $A$ to climb up the stairs while girl $B$ takes $15\ s$ for the same job. Compare the work done .
Answer
As height is the same for both girls $A$ and $B,$ work done is the same $($irrespective of time$)$
$\therefore$ Work done by $A :$ Work done by $ B = 1:1$