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July 23, 2014

July 23, 2014

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

-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!

- Physics -
**Elena**, Sunday, June 17, 2012 at 4:25am1. PE = W(fr)+KE

W(fr) =PE-KE=

=mgh - mv²/2 =

=2.5(9.8•350 - 60²•/2)=

= 4075 J.

PE =mgh = 2.5•9.8•350=8575 J.

W(fr)/PE =4075/8575 =0.48.

2. PE =mgh = 35•9.8•12 =4116 J.

k = PE/W =4116=5500 =0.75

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