When there is more than one force acting, we have considered the net force. It makes sense to consider the corresponding net work: Wnet = Fnet . Al when considering changes in energy. Take a look at the example below: GQ8.1 8/8 points (graded) An elevator is being lifted at a constant speed by a steel cable attached to an electric motor. Motor a) What can you say about the work done by the tension force of the cable, the work done by the force of gravity, and the net work done on the elevator? Also consider the change in kinetic energy. Cable v W gravity Negative Wtension: > Elevator Positive V V Zero V V ??: Zero V V b) Assume now that the same elevator is moving down and is slowing as it approaches the main floor. What can you say about the work done by the tension force of the cable, the work done by the force of gravity, and the net work done on the elevator? Also consider the change in kinetic energy. Wgravity Positive V V Wtension: Negative V V Wnet: Negative v V ??: Negative Q8.14 1/1 point (graded) In the figure, a constant external force P = 149 N is applied to a 20.0 kg box, which is on a rough horizontal surface. While the force pushes the box a distance of 9 m, the speed changes from 0.500 m/s to 2.21 m/s. What is the work done by friction during this process? Give your answer in Joules [J]). < 80 m > -1115 v -1115