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Help?

Hi all

Can't figure out how to do this question.

A pump rated at 600W is used to raise water from a lake to a height of 3m. If the pump delivers 600kg of water a minute with a velocity of 6.0ms-1, what is the efficiency of the pump?

Don't know where I should use the 600kg of water.


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Original post by cdoyle
Hi all

Can't figure out how to do this question.

A pump rated at 600W is used to raise water from a lake to a height of 3m. If the pump delivers 600kg of water a minute with a velocity of 6.0ms-1, what is the efficiency of the pump?

Don't know where I should use the 600kg of water.


This was posted from The Student Room's iPhone/iPad App


The water is being given kinetic and potential energy ½mv² and mgh
This is where the mass is used.
You are given a time of one minute, but remember, power in watt requires seconds.
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cdoyle
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Original post by Stonebridge
The water is being given kinetic and potential energy ½mv² and mgh
This is where the mass is used.
You are given a time of one minute, but remember, power in watt requires seconds.


High five! Was confused as the question was in my notes before they introduced ke and gpe. I was trying to convert 600kg to N for work done but couldn't get any further. Will try ke and gpe now.


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cdoyle
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2
Original post by Stonebridge
The water is being given kinetic and potential energy ½mv² and mgh
This is where the mass is used.
You are given a time of one minute, but remember, power in watt requires seconds.


What do I do after? Power is work done divided by time taken

Do I add ke and gpe? Wish the question had of been put at the very end of the notes. Would have made a bit more sense




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Yes, add the KE and PE gained by water in one second.
This is the power obtained from the motor.
This will turn out to be less than the 600W value given for the motor.
Then do you know what the efficiency would be.

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