Question

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?

Answer 1

MY ANSWERS (I only got 15 and 17).
15) The work done on the satellite by the gravitational force is zero because in space there are no forces/work acting upon an object [I don't get the second part].

17) More energy is required to walk up the stairs than to walk horizontally at the same speed because walking up the stairs has a horizontal and vertical component, which adds up to more distance than simply walking horizontally at the same speed.

Answer 2

Oh, and this one: Can the kinetic energy of an object be negative?

Answer 3

A satellite is in a circular orbit above Earth's surface. Why is the work done on the satellite by the gravitational force zero?

force is perpendicular to the displacement - no work is done.

Answer 4

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.

if speed doubles, KE quadruples, and thus work done to stop the car quadruples - what does this say about the stopping distance, if W = Fd ?

Answer 5

17) Explain why more energy is needed to walk up stairs than to walk horizontally at the same speed.

You're doing work against gravity.

Answer 6

@agent0smith, I got that part already, could you help me with the second part of #15?

Answer 7

What does the work-kinetic energy theorem predict about the satellite's speed?

work done = change in KE. no work done, no change in KE.... no change in speed.

Answer 8

Oh, and this one: Can the kinetic energy of an object be negative? no, it can either be 0 or positive. It's just a measure of how much energy an object has, due to it's mass and velocity

Answer 9

Thankss @agent0smith (:

Answer 10

@AllTehMaffs o w o

Answer 11

?

Answer 12

Help on #18?

Answer 13

18) set up a ramp problem, then write conservation of energy for it.

Answer 14

& is #15 from @agent0smith right?

Answer 15

15) agentsmith is right

"A satellite is in a circular orbit above Earth's surface. Why is the work done on the satellite by the gravitational force zero?

force is perpendicular to the displacement - no work is done."

"What does the work-kinetic energy theorem predict about the satellite's speed? " what do you think if no work is done on the satellite?

Answer 16

I dunno, it doesn't move ? c:
lol idk

Answer 17

It doesn't accelerate*?

Answer 18

"What does the work-kinetic energy theorem predict about the satellite's speed?

work done = change in KE. no work done, no change in KE.... no change in speed."


It's undergoing constant acceleration because it's circular motion

Answer 19

Don't you mean constant velocity?

Answer 20

nope - it's velocity is not constant. It's undergoing centripetal acceleration at all times.

it's speed is constant.

Answer 21

~Its

Answer 22

Centripetal?
How is the speed constant if its velocity isn't?

Answer 23

velocity is a vector quantity. Since the object is in a circular motion, it is changing direction at any moment in time. so the velocity is changing, which means there is an acceleration.

Answer 24

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Answer 25

velocity is changing only in terms of direction. nothing else. speed remains constant because since speed is a scalar quantiy, the change in direction doesnt effect its value.

Answer 26

Oh. Right. Thanks for reminding me @xxyyxyyx

Answer 27

Guys give a medal to each other lol

Answer 28

for 18, you should make up a ramp problem and analyze it with and without friction

Answer 29

write out conservation of energy for both of em.

Answer 30

Hold up