posted by Tim on .
An object of mass .550kg is lifted from the floor to a height of 3.5m at a constant speed. How much work is done by the lifting force (include units)?
b.) How much work is done by the Earth on the object?
c.) What is the net work done on the object?
d.) What is the change in kinetic energy of the object?
e.) Are your results consistent with the work-energy principle? Explain.
a) m g h = .55 * 9.81 * 3.5 = 18.9 Joules
b) force down, displacement up --> -18.9 J
c) the work done by the lifting force exactly matched the work done by gravity so no net work was done
d)assuming it was moving at constant speed throughout the problem, there was no change in kinetic energy.
e) the work done by our lift force exactly matched that done by gravity. If we only considered the work done by the lift force, we would say the potential energy in the gravitational field increased by m g h.