The energy expended during move can be calculated using the Definition of Work, that is given by:
[tex]E=P\Delta S[/tex]
Using the Definition of Potence, comes:
[tex]P_{ot}= \frac{P}{\Delta t} \\ \Delta t = \frac{P\Delta S}{P_{ot}}[/tex]
Entering the unknowns, we have:
[tex]\Delta t = \frac{P\Delta S}{P_{ot}} \\ \Delta t = \frac{50*9.8*8}{4*10^2} \\ \boxed {\Delta t =9.8s}[/tex]
Number 2
If you notice any mistake in my english, please let me know, because i am not native.
