Science > Physics > what happens when you shoot a ball from a riding train?
| Topic: |
Science > Physics |
| User: |
"Bert" |
| Date: |
01 Dec 2004 01:02:54 PM |
| Object: |
what happens when you shoot a ball from a riding train? |
The next question is asked in a popular Dutch science-quiz:
While passing a station, a train rides with 50 kilometers per hour from
the beginning to the end of a 100 meter long platform. Halfway through
you shoot a tennisball with 50 kilometers per hour backwards from the
back of the last car. Where will the ball end?
A. around the beginning of the platform
B. around the centre of the platform
C. around the end of the platform
So, summarized:
- You shoot the ball (from the train) when you're in the middle of the
platform
- You shoot the ball in the direction that you came from
(Imagine the beginning is A and the end is B
the train moves from A to B, from left to right)
At first I thought the ball would 'drop dead' and land around the center
of the platform. Because you shoot the ball with the same velocity as
the train moves, but in another direction. Add the two velocities and
zero kph would be the result.
But when I think longer about it: When you shoot the ball from the train
you're not only adding energy to the ball, but also to the train in the
other direction. This energy is provided by yourself (or maybe by using
a tennisgun). In this case half of the energy is released to the left
and half of it is released to the right.
Still, I cannot figure out what the consequence is for the speed of the
ball in relation to the platform. Can someone help me out or give me
hint? I have the idea that A would be the correct answer, but I cannot
explain...
Then, there's also the draft of air behind the train. The windspeed
right at the back of the train will also be 50 kph. Due to friction this
will tend to move the ball to the right (B)
Bert
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| User: "Mishnuc" |
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| Title: Re: what happens when you shoot a ball from a riding train? |
01 Dec 2004 01:59:40 PM |
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"Bert" <bert@bytegraag.nl> wrote in message
news:41AE155D.5A5618DF@bytegraag.nl...
The next question is asked in a popular Dutch science-quiz:
While passing a station, a train rides with 50 kilometers per hour from
the beginning to the end of a 100 meter long platform. Halfway through
you shoot a tennisball with 50 kilometers per hour backwards from the
back of the last car. Where will the ball end?
A. around the beginning of the platform
B. around the centre of the platform
C. around the end of the platform
So, summarized:
- You shoot the ball (from the train) when you're in the middle of the
platform
- You shoot the ball in the direction that you came from
(Imagine the beginning is A and the end is B
the train moves from A to B, from left to right)
At first I thought the ball would 'drop dead' and land around the center
of the platform. Because you shoot the ball with the same velocity as
the train moves, but in another direction. Add the two velocities and
zero kph would be the result.
But when I think longer about it: When you shoot the ball from the train
you're not only adding energy to the ball, but also to the train in the
other direction. This energy is provided by yourself (or maybe by using
a tennisgun). In this case half of the energy is released to the left
and half of it is released to the right.
Still, I cannot figure out what the consequence is for the speed of the
ball in relation to the platform. Can someone help me out or give me
hint? I have the idea that A would be the correct answer, but I cannot
explain...
Then, there's also the draft of air behind the train. The windspeed
right at the back of the train will also be 50 kph. Due to friction this
will tend to move the ball to the right (B)
Bert
If you ignore spin, wind resistance, gravity, elevation, and velocity and
side angle errors (which are not specified in the problem) then it must be
center. It doesn't matter how long the platform is, does it?
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| User: "AaronB" |
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| Title: Re: what happens when you shoot a ball from a riding train? |
01 Dec 2004 06:10:13 PM |
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Bert <bert@bytegraag.nl> wrote in message news:<41AE155D.5A5618DF@bytegraag.nl>...
The next question is asked in a popular Dutch science-quiz:
While passing a station, a train rides with 50 kilometers per hour from
the beginning to the end of a 100 meter long platform. Halfway through
you shoot a tennisball with 50 kilometers per hour backwards from the
back of the last car. Where will the ball end?
A. around the beginning of the platform
B. around the centre of the platform
C. around the end of the platform
So, summarized:
- You shoot the ball (from the train) when you're in the middle of the
platform
- You shoot the ball in the direction that you came from
(Imagine the beginning is A and the end is B
the train moves from A to B, from left to right)
At first I thought the ball would 'drop dead' and land around the center
of the platform. Because you shoot the ball with the same velocity as
the train moves, but in another direction. Add the two velocities and
zero kph would be the result.
But when I think longer about it: When you shoot the ball from the train
you're not only adding energy to the ball, but also to the train in the
other direction. This energy is provided by yourself (or maybe by using
a tennisgun). In this case half of the energy is released to the left
and half of it is released to the right.
Still, I cannot figure out what the consequence is for the speed of the
ball in relation to the platform. Can someone help me out or give me
hint? I have the idea that A would be the correct answer, but I cannot
explain...
Then, there's also the draft of air behind the train. The windspeed
right at the back of the train will also be 50 kph. Due to friction this
will tend to move the ball to the right (B)
Bert
I believe the intention of the problem is to state that the ball would
land in the centre, as your previous logic suggests. Due to certain
other specific elements (air resistance, etc), there could be some
slight changes exactly where it lands, but addition of velocities
would indicate that regardless of these factors, it will land CLOSEST
to the centre. Interestingly, the problem is a bit silly since we
don't know the height of the train: without it, we have no way of
determining, were it either of the other cases, whether or not it
would land even remotely close to the end of the platform.
A.
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| User: "pete" |
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| Title: Re: what happens when you shoot a ball from a riding train? |
10 Dec 2004 07:40:05 AM |
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Bert wrote:
you're not only adding energy to the ball,
You're not adding any energy to the ball.
You're stopping the ball.
The ball has the same initial velocity as the train.
--
pete
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