A man lifts a 15 kg crate from thefloor to a shelf (5 m high) at constantspeed *

Question

A man lifts a 15 kg crate from thefloor to a shelf (5 m high) at constantspeed*.
(*Neglect the very start and very end of the lift, where thecrate would of course need to be accelerated from/torest.)


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

b.) What is the change in the PE of the crate?
J c.) If it takes 3 sfor the man to lift the crate to the shelf, find the man's poweroutput.
W


A man lifts a 15 kg crate from thefloor to a shelf (5 m high) at constantspeed*.
(*Neglect the very start and very end of the lift, where thecrate would of course need to be accelerated from/torest.)


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

b.) What is the change in the PE of the crate?
J c.) If it takes 3 sfor the man to lift the crate to the shelf, find the man's poweroutput.
W

Explanation / Answer

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

      Change in KE = 0J

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

                 change in PE = m g h = 15 * 9.8 * 5 =735 J

c.) If it takes 3 sfor the man to lift the crate to the shelf, find the man's poweroutput.
W

                      P =   change in PE / time
                         = 735 / 3
                         = 245 W

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