Work and Potential Energy Problem

[bengaltiger14]

Homework Statement

A 140 Watt motor (70% efficient) is available to raise a load 5 meters into the air. If the task takes 5 seconds to complete, how heavy was the load in kilograms?


I first determine the motot output: 140W * 70% == 98 Watts

I then multiply 98 Watts by 5 seconds to get PE = 490Joules

Now, setting 490Joules = mgH and solving for m, I get 10 kilograms

The answer is supposed to be 110kg according to my professor but I cannot get to that number. What am I doing wrong?

Thanks

 

[Doc Al]

Your answer looks good to me. I don't think you did anything wrong. (Ask your professor to show her solution.)