Physics, electric power, Input, output and efficiancy.? : Eco Answers

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Question by : Physics, electric power, Input, output and efficiancy.?
Please help me with this question:

A small electric motor rotates a shaft, which winds up a thread attached to a 3.0 N weight. The weight is lifted through 1.0m in 4.0s. Find the motors output.
If the motor takes 0.5A from a 6.9 V supply, find the power input and the motors efficiency. What are the most likely causes of “lost power”?

Please can you explain it as i am stuck abit with this type of question. Thanks alot.

Best answer:

Answer by billrussell42
What is the PE (Potential Energy) gained by the lifted weight?
PE = mgh = wh = 3×1 = 3 joules

dividing by time gets you power
P = 3 J / 4s = 0.75 watts

Electrical power = EI = 6.9 x 0.5 = 3.45 watts

Efficiency is output power / input power = 0.75 / 3.45 = 21.7%

The rest of the power would show up as heat.

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