|MadSci Network: Physics|
Here is our problem. A 5hp electric motor is used to operate a small elevator at a construction site. The motor, which is 60% efficient, lifts a load of 15 kN (including the platform) to a height of 20m. a. How much work is done? w = F * s = 15kN * 20m = 300,000 J b. How much electrical energy must be supplied to the motor? E = output / input .6 = 300,000 / x x = 500,000 J c. How long does it take to reach the 20 m height? * This is where the problem occured. Which energy do you use 300,000 J or 500,000 J If you use 300000 J (that's what we(students used)) P = W / t = 300000/t = 3730 t= 80.4 sec If you use 500000 J (that's what the teacher used) t= 134 sec
Re: How would you calculate the time needed to lift an object?
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