An electric motor is required to raise 400kg of water through a vertical height of 120m in 2min
What will be electric power required) If the overall efficiency is 80%
a) 3.2 KW
b) 5 KW
c) 32 KW
d) 300 KW
Answers
Answer:
Explanation:
When you turn this in, do we share an A grade?
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The work done to lift the weight is Force X displacement.
The force on the 400kg mass is gravity and so the weight is 4000 Newtons.
The displacement is 1200 meters, so the work done is 4.8 X 10^6 joules.
But the motor is doing more work because it is 80% efficient. The work done by the motor is the work done on the mass divided by 0.8. or 6.0 X 10^6 joules.
Power is the rate of energy into the motor. So 6 X 10^6 joules is done in 2.0 minutes, or 120 seconds. The power is 6 X 10^6 joules / 120 seconds or 50 X 10^3 watts. 50 kilowatts.
Oh also, this assumes that the mass has no appreciable velocity after it reaches the top of the mine shaft. If it does, then the work done on the mass will be greater, by an amount sufficient to give the mass kinetic energy.
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This problem requires knowledge of:
Work, rate of work, i.e. power, minutes to seconds conversion, and the relationship between work done and work into a motor of efficiency 0.8. But mostly it requires the student to think rationally.
As you learn, you should parse each new problem and ponder each step. Other problems will be different combinations of these principles. The process is getting a fund of knowledge (like minutes to seconds conversion) and rational combinations of these principles. Once you have mastered the combining of principles, the easy part is learning new principles. It is the rational, logical combining of the principles which will lead you to become an engineer. Logical thinking is what you should hone. You can look up things like minutes to seconds conversion anytime.