A 50 kg box is raised by an elevator system to a position 10 m high.
A) how much work is done on the box?
B) because of friction losses an electric motor must generate a force of 800 N to raise the box. How much work does the motor do while raising the box?
C) if it takes 20 seconds to raise the box what is the power output of the motor?
D) when the box reaches the top it is transferred to a horizontal conveyor which carries the box 20 meters. How much work is done on the box by the horizontal conveyor?

Question

A 50 kg box is raised by an elevator system to a position 10 m high. 
A) how much work is done on the box?
B) because of friction losses an electric motor must generate a force of 800 N to raise the box. How much work does the motor do while raising the box?
C) if it takes 20 seconds to raise the box what is the power output of the motor?
D) when the box reaches the top it is transferred to a horizontal conveyor which carries the box 20 meters. How much work is done on the box by the horizontal conveyor?

matt101 · Answer

A) By conservation of energy, the work done on the box is equal to the gravitational potential energy the box gains, mgh.

B) Another definition of work is force times distance over which the force is applied (W=Fd). You can use this relationship to calculate work.

C) Power refers to the energy expenditure over time, in this case, P=W/t. You calculated work in the previous question and have time given, so use this information to find power.

D) The work done by the conveyor belt can also be found using W=Fd. The force in this case is going to be the frictional force, but you need additional information to calculate what that force would be (e.g. the coefficient of static friction).