Question

An electric motor has a rating of 4.0 × 10^2 watts.
How much time will it take for this motor to lift a
50.-kilogram mass a vertical distance of 8.0 meters?

Answer 1

Can i help

Answer 2

hint:
power \(W\) is the work done by an external force over time, so we can write:
\[\Large W = \frac{L}{{\Delta t}}\]
now, the work done by the motor, is equal to the work done by gravity, so we can write:
\[\Large L = mgh\]
where \(h=8\) is the vertical displacement. Therefore after a substitution, we get:
\[\Large W = \frac{L}{{\Delta t}} = \frac{{mgh}}{{\Delta t}}\]
and finally:
\[\Large \Delta t = \frac{{mgh}}{W} = \frac{{5 \cdot 9.81 \cdot 8}}{400} = ...\sec \]

Answer 3

Remember units :
Watt is J/s , also you get seconds in answer. Unit of mgh is J (joule)