Hovercraft B/C

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Re: Hovercraft B/C

Postby UTF-8 U+6211 U+662F » March 14th, 2018, 2:35 pm

Oh whoops, haha.
Find the final speed of a 100 kg roller coaster car that has dropped 50 m (from rest), gone back up 30 m, dropped 60 m, gone back up 30 m, and then at that level been pushed for 5 seconds with a force of 50 Newtons.
2.5 m/s
No, not quite. Remember that the car has dropped and therefore gained speed.

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Re: Hovercraft B/C

Postby MattChina » March 14th, 2018, 3:16 pm

Oh whoops, haha.
Find the final speed of a 100 kg roller coaster car that has dropped 50 m (from rest), gone back up 30 m, dropped 60 m, gone back up 30 m, and then at that level been pushed for 5 seconds with a force of 50 Newtons.
2.5 m/s
No, not quite. Remember that the car has dropped and therefore gained speed.
33.8m/s?
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Re: Hovercraft B/C

Postby UTF-8 U+6211 U+662F » March 14th, 2018, 3:18 pm

2.5 m/s
No, not quite. Remember that the car has dropped and therefore gained speed.
33.8m/s?
Yep (at least that's what I remember). Your turn!

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Re: Hovercraft B/C

Postby MattChina » March 14th, 2018, 3:39 pm

A hovercraft with a mass of 100 kg going at 4m/s has its thrust turned off abruptly. It is traveling across the ice with a friction coefficient of 0.38. How far will it travel across the ice?
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Re: Hovercraft B/C

Postby UTF-8 U+6211 U+662F » March 14th, 2018, 6:53 pm

A hovercraft with a mass of 100 kg going at 4m/s has its thrust turned off abruptly. It is traveling across the ice with a friction coefficient of 0.38. How far will it travel across the ice?
a = 9.8 m/s^2 * 0.38 = 3.724 m/s^2
0 = (4 m/s)^2 - 2 * 3.724 m/s^2 * d
d = 2.15 m

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Re: Hovercraft B/C

Postby MattChina » March 14th, 2018, 7:26 pm

A hovercraft with a mass of 100 kg going at 4m/s has its thrust turned off abruptly. It is traveling across the ice with a friction coefficient of 0.38. How far will it travel across the ice?
a = 9.8 m/s^2 * 0.38 = 3.724 m/s^2
0 = (4 m/s)^2 - 2 * 3.724 m/s^2 * d
d = 2.15 m
Correct. Your Turn.
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Re: Hovercraft B/C

Postby UTF-8 U+6211 U+662F » March 14th, 2018, 7:32 pm

An elastic collision happens over a period of five seconds, between a 1 kg ball and a 5g pencil. What is the average force exerted on the pencil?

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Re: Hovercraft B/C

Postby Justin72835 » March 14th, 2018, 9:08 pm

An elastic collision happens over a period of five seconds, between a 1 kg ball and a 5g pencil. What is the average force exerted on the pencil?
Do you need to know anything about initial and final velocities to solve this question?
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Re: Hovercraft B/C

Postby UTF-8 U+6211 U+662F » March 15th, 2018, 1:45 pm

An elastic collision happens over a period of five seconds, between a 1 kg ball and a 5g pencil. What is the average force exerted on the pencil?
Do you need to know anything about initial and final velocities to solve this question?
Whoops: They are moving toward each other, the ball with a speed of 5 m/s and the pencil with a speed of 0.4 m/s.

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Re: Hovercraft B/C

Postby Justin72835 » March 15th, 2018, 2:18 pm

An elastic collision happens over a period of five seconds, between a 1 kg ball and a 5g pencil. What is the average force exerted on the pencil?
Do you need to know anything about initial and final velocities to solve this question?
Whoops: They are moving toward each other, the ball with a speed of 5 m/s and the pencil with a speed of 0.4 m/s.
Alright, first find the final velocities of both of the objects. 





Plugging in the given values and solving for the final velocities gives 4.946 m/s for the ball and 10.346 m/s for the pencil. Now you can find the average force on the pencil:



This gives an average force of 0.0107 N. You can check this answer by doing the same calculation on the ball (Newton's Third Law).
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