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?
[Assume 100% efficiency.]
(1) 0.98 s (3) 98 s
(2) 9.8 s (4) 980 s

Answer 1

The energy expended during move can be calculated using the Definition of Work, that is given by:


`E=P\Delta S`

Using the Definition of Potence, comes:


`P_(ot)= (P)/(\Delta t) \\ \Delta t = (P\Delta S)/(P_(ot))`

Entering the unknowns, we have:


`\Delta t = (P\Delta S)/(P_(ot)) \\ \Delta t = (50*9.8*8)/(4*10^2) \\ \boxed {\Delta t =9.8s}`

Number 2

If you notice any mistake in my english, please let me know, because i am not native.