Hovercraft B/C

[UTF-8 U+6211 U+662F]

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]

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.

retry (Click to Show Hidden Text)

33.8m/s?

[UTF-8 U+6211 U+662F]

2.5 m/s

No, not quite. Remember that the car has dropped and therefore gained speed.

retry (Click to Show Hidden Text)

33.8m/s?

Yep (at least that's what I remember). Your turn!

[MattChina]

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?

[UTF-8 U+6211 U+662F]

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?

Click to Show Answer

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]

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?

Click to Show Answer

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.

[UTF-8 U+6211 U+662F]

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?

[Justin72835]

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?

[UTF-8 U+6211 U+662F]

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]

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.

Click to Show Answer

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).