# Tennis Ball Collide With Train Prob.

#### Delzac

hi all,

the qns is when a tennis ball collide with a train, can the ball stop the train for a split sec, since during collision, the ball have to change direction so velocity at some point in time is equal to zero. Being at V= 0 for that split sec, and since the ball is in contact with the train, we can deduce that the train also stop temporaryly.

I know the qns has been ask B4. At that time, the answer given was that acceleration for the change of velocity is infinity, so V can nv be zero.

Now the REAL qns is how do u prove it mathematically(not logically)
that acceleration is infinity?

P.S. i tried to search for the thread but couldn't find it.(honest)

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#### J77

A quick search for train gives: https://www.physicsforums.com/showthread.php?t=125266&highlight=train

Definitive post:
Dave said:
I'm just going to say this one last time, and then y'all can do whatever you want.

There is no such thing as a perfectly rigid body. If the tennis ball and train were both perfectly rigid, we would definitely have a problem. The energy required to reverse the direction of one perfectly rigid body by another perfectly rigid body would be infinite - as would the acceleration rates.

And with infinite energy kicking around, bringing the train to a halt would be the most trivial of concerns. Note that neither the train nor the ball would be able to vapourize, or do any other such thing that would require the transfer of energy between atoms - which they can't do since they are perfectly rigid. And, since we have things changing direction without loss or gain of energy, kinetic or otherwise, we've also eliminated inertia. But I digress...

You can see how this universe rapidly deteriorates into a fantasy.

Bodies interact (transfer kinetic energy) over a non-zero distance and a non-zero time.

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#### Delzac

haha thx for helping me find the tread i understand it now

#### DaveC426913

Gold Member
Hey! I've been quoted!

"Tennis Ball Collide With Train Prob."

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