Question

A boy of mass $m$ climbs up a staircase of vertical height $h$. What would have been the work done if he uses a lift in climbing the same vertical height?

• A. $\frac{mg}{h}$
• B. $mh$
• C. $0$
• D. $mgh$

Answer 1

The correct option is D $mgh$

Here while boy is in the lift we will have a force of $m\times g$.
As the force and displacement are in opposite direction there will be an angle of 180 degree between them.
We know that $W=F\times S\cos \theta$.On substituting we get $F=m\times g\times h\cos {180}^o=-m\times g\times h$.
Hence lift does a work of $m\times g\times h$ against to gravity.