A motor lifts a 450 kg load through 8.0 m in 20 s at a steady speed.
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A motor lifts a load through in at a steady speed. Taking , what power does it give?
Need a reminder? The key ideaShow
Power is the rate of doing work: , in watts. For a force at speed , . Efficiency useful power out power in. One kilowatt-hour is .
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Plan. .
Step 1. Work. .
Step 2. Power. .
Answer: , about .
Check. The speed is , and . Same.
Watch out. At a steady speed there is no kinetic energy to add; the work all goes into potential energy.
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