- #1
physicskillsme
- 24
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Could someone check I have these setup right and check my answers - if not where have I gone wrong.
How long will it take a 50 hp motor to do 1 MJ of work?
1hp=746W = 50*746=37300W
1 MJ = 1000000J / 37300W = 26.8 secs
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A 650 W microwave oven is used to reheat food for one minute. How much energy is supplied?
W=p*t = 39000=650*60
Answer: 39000J
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How much energy is required to heat 600 g of copper from 22 oC to 50 oC?
Specific Heat Copper = 385J/Kg Kelvin
Q=m*c*deltaT
Q=.6*385*28
Q=6468J
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You push as hard as you can for 6 seconds on a crate of mass 250 kg, but are unable to move it. What is your rate of doing work (power)?
W=Fd
But in this case nothing is moving so I'm not doing any work - is that right?
-----------------------------------------------------
Finally what is the best way of setting this one up?
The immersion heater in an electric hot water system is rated at 9 kW. If the tank is initially filled with 40 gallons (about 150 litres, with a mass of 150 kg) of cold water at 15 oC, how long will it take the heater to raise the temperature to 40 oC?
Thanks
How long will it take a 50 hp motor to do 1 MJ of work?
1hp=746W = 50*746=37300W
1 MJ = 1000000J / 37300W = 26.8 secs
-----------------------------------------
A 650 W microwave oven is used to reheat food for one minute. How much energy is supplied?
W=p*t = 39000=650*60
Answer: 39000J
-----------------------------------------
How much energy is required to heat 600 g of copper from 22 oC to 50 oC?
Specific Heat Copper = 385J/Kg Kelvin
Q=m*c*deltaT
Q=.6*385*28
Q=6468J
------------------------------------------
You push as hard as you can for 6 seconds on a crate of mass 250 kg, but are unable to move it. What is your rate of doing work (power)?
W=Fd
But in this case nothing is moving so I'm not doing any work - is that right?
-----------------------------------------------------
Finally what is the best way of setting this one up?
The immersion heater in an electric hot water system is rated at 9 kW. If the tank is initially filled with 40 gallons (about 150 litres, with a mass of 150 kg) of cold water at 15 oC, how long will it take the heater to raise the temperature to 40 oC?
Thanks