Jabababa said:
oh ok now i get it, if its 100% efficient its at 5.292 seconds...so if its at 0% then its not going to do anything. Then 25% is between 100% and 0% then it must take longer, 21seconds.
...so my 1st answer was right...anyways thanks for the help. Sorry if i snapped before and offended you. Its almost 5am, haven't gotten any sleep.
It is always useful to break the question into parts, like I indicated, so you can assess if the answers you are getting are reasonable.
It is very easy to make a slip and multiply by 1/4 rather than divide, but if you calculate on the way you should notice.
While re-arranging the formulae the substituting gives an answer you often don't know whether it is reasonable.
What I would have done is a rough check using g = 10 for simplicity, and a height of 10m.
mgh then becomes 45 x 10 x 10 = 4500.
With a 1000W motor that would take 4.5 seconds.
25% efficiency would means 4 times as long - or 18 seconds.
[note that all those figures can be calculated as mental arithmetic - no calculator needed].
Now reality: g is a little less than 10, and the height is a little less than 10 - so the time would be smaller. But the motor is only a nominal 750W so that would make it longer. SO I expect an answer about 20 seconds.
Your formula manipulation gave 21, so I would have been happy with that figure.