Could someone check I have these setup right and check my answers - if not where have I gone wrong.(adsbygoogle = window.adsbygoogle || []).push({});

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

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Could you check these for me - please

**Physics Forums | Science Articles, Homework Help, Discussion**