Work + energy: conceptual questions. 15) a satellite is in a circular orbit above earth's surface. why is the work done on the satellite by the gravitational force zero? what does the work-kinetic energy theorem predict about the satellite's speed? . 16) a car traveling at 50.0 km/h skids a distance of 35 m after its brakes lock. estimate how far it will skid if its brakes lock when itsinital speed is 100.0 km/h. what happens to the car's kinetic energy as it comes to rest? . 17) explain why more energy is needed to walk up stairs than to walk horizontally at the same speed. 18) how can the work-kinetic energy theorem explain why the force of sliding friction reduces the kinetic energy of a particle?

For number 15, the work that was done on the satellite force is zero because in space, there are no other forces or work that is acting upon an object. Based on the work-kinetic energy theorem, there was no change in speed of because there was not work done and change in kinetic energy.

For number 16, 
W = d (K.E.)
35/d = (50)²/(100)²
35/d= 1/4
d= 35 x 4
d= 140 m

It will skid for 140 meters. Based on the law of the conservation of energy, kinetic energy is converted into sound, heat, and motion once the car goes to a complete stop.

For number 17, the energy required to walk up the stairs is higher compared to walking in a horizontal plane at the same speed because walking up the stairs has both vertical and horizontal components which adds up more distance. Walking up the stairs is doing work against gravity.

For number 18, Wfnet = delta KE
The equation of work energy theorem states that particle speed becomes lowers as the force of sliding friction is the only force that is acting on the object.

The correct answers to these questions are:
15. Work = 0. The reason why is because in space, there are no other forces or work that is acting upon an object. 
16. d = 140 m
W = d (K.E.)
35/d = (50)^2 / (100)^2
35/d = 1/4
d= 35 * 4
d= 140 m
17. There is more energy used in walking up the stairs than walking in a horizontal plane given the same speed. Walking up the stairs is doing work against gravity.
18. Wfnet = delta KE

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