physics
posted by chris .
A box weighing 100 newtons is pushed up an inclined plane that is 5 meters long. It takes a force of 75 newtons to push it to the top,which has a height of 3 meters. What is the efficiency?

Divide the potential energy change (100 N x 3 m)) by the work done (75 x 5 J).

100x3=300 75x5=375
300/375=.80 or 80% 
Why do we cross multiply. I though you multiply 100 x 5 then 75 x 5 and then divide and multiply by 100

the formula for potential energy is mass * acceleration of gravity* height. not mass * height

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