Question

a person pulls a cart at 4.5 m/s and pushes it with a force 20 N [east]. What is the power exerted by the person.

Answer 1

A simple derivation. Power is the amount of energy spent per unit time (or teh work done per unit time). that is \[P=\frac{E}{t}\] But we know that the work done in pushing an object with a force F, over a distance d is (which is the energy put into a system) is given by \[E=Fd\]Hence\[P=\frac{Fd}{t}=F\times \frac{d}{t}\]But we know that the velocity is \(v=d/t\), and hence we get that \[P=F\times v\].

Form this equation plug in the numbers and you can get \(P=20\times 4.5=90\) Watts.