Posted by **lenny** on Sunday, June 17, 2012 at 3:34am.

1. A 2.5kg rock is dropped from a 350m cliff. It hits the ground with a speed of 60 m/s. What percent of its mechanical energy was lost to air resistance?

-the answer is 48%

2. A motor uses 5500J to lift a 35kg object a vertical distance of 12m. What is the efficiency of the motor?

-the answer 0.75

I need help, Thanks!

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