120/30 = 4 Newtons/meter weight
How far up did we move the center of gravity of the chain?
at the start it was 15 meters below drum
at the end 9 meters was at the drum and 21 meters (84 Newtons weight) was below drum with center at 10.5 meters below
so if I call the drum height h = 0
then at start m g h = 120 (-15) = -1800 Joules
at finish I have 0 for stuff up there and mgh = 84 * -10.5) = - 882 Joules
so my gain in gravitational Potential energy is
-882 + 1800 = 918 Joules
That had to come from the winch :)
A chain that is 30 m long and weighs 120N.m hangs from the drum of a winch.
Determine the work to wind the first 9m of the chain .
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