Question

The crane lifts a 100kg block of sugar through a vertical height of 16m in 20s. If the power supplied to the motor driving the crane is 1kw, what is the efficiency of the motor?

Answer 1

I tried this:

Explanation:

We can evaluate the Power needed for the crane to lift our cube by considering:
`P_(out)="Work"/"time"`
where the work will go to increase the Gravitational Potential Energy `U` of the system or:

`W=U=mgh`

so:

`P_(out)=(mgh)/t=(100*9.8*16)/20=784W`

Efficiency will be:

`eta=P_(out)/P_("in")=784/1000=0.784` or `78.4%`.