## Hovercraft B/C

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### Re: Hovercraft B/C

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.

MattChina
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### Re: Hovercraft B/C

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

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

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

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

MattChina
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### Re: Hovercraft B/C

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

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

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

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.

Justin72835
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### Re: Hovercraft B/C

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.

$m_1v_{1i}+m_2v_{2i}=m_1v_{1f}+m_2v_{2f}$

$v_{1i}-v_{2i}=v_{2f}-v_{1f}$

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:

$F\Delta t=m\Delta v=F*5=0.005(10.346-(-0.4))$

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).
"The fault, dear Brutus, is not in our stars,
But in ourselves, that we are underlings."

University of Texas at Austin '23
Seven Lakes High School '19