A man lifts a 3 kg crate from the floor to a shelf (2 m high) at constant speed*

Question

A man lifts a 3 kg crate from the floor to a shelf (2 m high) at constant speed*.
(*Neglect the very start and very end of the lift, where the crate would of course need to be accelerated from/to rest.)



d.) What was the change in KE of the crate?
?J

e.) What is the change in the PE of the crate?
J

f.) Is mechanical energy conserved in this process? Explain.

g.) Is the force the man exerts a conservative force?
yes
no

Explain.

h.) If it takes 5 s for the man to lift the crate to the shelf, find the man's power output.
?W

Explanation / Answer

0. It has no more KE. PE = mgh= 2*9.8*3. It depends if there is friction. I'd say no, because at the top, it stops moving, so loses KE = friction takes it all. yes. It's similar to how gravity acts. power = work/time = 2*9.8*3/5=11.76

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