Question

NOTE: 1 MJ = 106J.
One of the most powerful cranes in the
world, operating in Switzerland, can slowly
raise a load of 6000 tonne to a height of 8 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

Answer 1

work = force * distance
= 6000 * 1000kg * 9.81 * 8
= 470.88 * 10^6 J
= 471.88 MJ

Answer 2

Since the load moves at constant speed the force applied by the engine is equal to the gravity force. Therefore, the work is
W=F•h = m•g•h =6•10^6•9.8•8=
= 4.71•10^8 J=471 MJ