Homework Help: Physics

Posted by Danny on Tuesday, February 26, 2013 at 10:03am.

One of the most powerful cranes in the
world, operating in Switzerland, can slowly
raise a load of 6000 tonne to a height of 12 m.
(1 tonne = 1000 kg)
The acceleration of gravity is 9.81 m/s2 .
How much work is done by the crane?
Answer in units of MJ
I found it by using Work = mass* acceleration* distance
1) converted 6000 tones to kilograms and I got 6000000kg thus,
2) work = (6000000kg)*(9.81m/s^2)*(12m)=706320000J
3)Then I converted 706320000j to MJ
706320000/10^6=70632 MJ
002 (part 2 of 2) 5.0 points
If it takes 3 min to lift the load at constant velocity to this height, find the power developed
by the crane.
Answer in units of MW.
please help me I have tried it 3 times and it's wrong. Please explain so I can understand how to go about this problems.

Physics - Henry, Thursday, February 28, 2013 at 12:28pm
Mass=6*10^3tons * 1*10^3kg/ton=6*10^6kg.

Work = F*h = mg*h.
Work = 6*10^6*9.81 * 12=706.3*10^6 J. =
706.3 MJ.

P = Work/T = 706.3MJ/180s. = 3.92 MJ/s.=
3.92 MW.

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