Question

An electric motor has a rating of 4.0 × 10^2 watts.

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:

$P_{ot}= \frac{P}{\Delta t} \\ \Delta t = \frac{P\Delta S}{P_{ot}}$
 
     Entering the unknowns, we have:

$\Delta t = \frac{P\Delta S}{P_{ot}} \\ \Delta t = \frac{50*9.8*8}{4*10^2} \\ \boxed {\Delta t =9.8s}$

Number 2

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