Question

A porter lifts a suitcase weighing 20 kg from the platform and puts it on his head 2.0 m above the platform. Calculate the work done by the porter on the suitcase.

Answer 1

The kinetic energy of the suitcase was zero when it is was at the platform and it aain became zero when it was put on the head. The change in kinetic energy is zero and hence the total work done on the suitcase is zero. Two forces act on the suitcase, one due to gravity and the other due to the porter. Thus, the work done by the porter is negative of the work done by gravity. As the suitcase is lifted up,the work done by gravity is `W=-mgh`
`=-(20 kg)(9.8m/s^2)(2m)=-392J`. The work done by the porter is 392 J =390 J.