Impossible quiz

strike the train?

 

You're soooo close. If I keep giving clues I'd have to tell you anyway. It's an old problem and, like I said, I've never got a truly satisfactory answer.

The ball hits the train and rebounds. But to rebound it must stop moving and reverse direction. The point at which the ball stops moving is also the point at which it is in contact with the train. If the ball is stopped and it is in contact with the train then, logically, the train must be stopped as well.

Over to you david (and sorry everybody for the nasty question...)

 

No, the ball bearing only stopped relative to the train. Not relative to an observer on the platform.The train is still travelling through the station, therefore the ball bearing is already (at the exact moment of impact) travelling at the same speed & direction as the train itself. Its effect would be to slow the train down by an immeasurably small ammount.

This arguement is similar to elements of Einstein's theory of relativity pertaining to the speed of light, if you are familiar with it.




Next question... Who wrote "The Trumpet Major"?

No Googling or similar form of cheating for a minimum of 48hrs please.

 

I am (having done degree-level physics, but this was"too trivial" for the tutors ) but:
the ball must halt before it can reverse direction. It is impossible for the ball to go from, say 10 metres/sec forwards to 10 metres/ sec backwards without, at some point, being at zero speed even relative to an observer.

 

That would be true if striking a stationary object, but not a moving one.

 

It is true for a moving object as well.
But I know the answer.
I kept me awake until I got it.....
The original question is predicated on a flawed assumption, and I'm keeping the secret to annoy future students

 

Unless I am completely misunderstanding the scenario of the train & ball bearing, my last comment stands as fact.

 

Draw the velocity diagram. The ball, to reverse direction MUST halt, relative to whatever viewpoint you care to choose (except the ball itself where it's not moving at all).

 

Yes, but if you draw the same graph for the moving object, unless it's a very small object or a very large ballbearing you will probably not notice any significant change in velocity at all, so the only thing you are in actual fact stopping (Even if only for a miniscule fraction of a second) is the ballbearing not the vehicle. :-?

Just because the ball bearing stops even if only for the tiniest fraction of a second before changing direction doesn't mean that the object it hits does as well unless it too reverses direction or the impact energies cancel one another out and it actually stops dead.

Perhaps I'm wrong but it seems to me that the flawed assumption is that the vehicle must be affected in the same manner as the ballbearing.

 

Simon has it: the assumption is that "the train" is an indivisible unit. The ball bearing MUST stop (it is physically impossible for anything to reverse direction without having zero velocity in the original direction of travel at some point), and if it's in contact with the train then the train must also be stopped.
What actually happens is that PART of the train stops - because the ball bearing and the small part of the train that is hit will both "give" to a slight degree (for example a rubber ball will flex greatly as each part of it stops consecutively, a totally rigid component would just shatter as it stops). So the bearing will deform and then reboumd and the portion of the train that is hit will also deform and then rebound (leaving "dint marks"). Actual flexion depends entirely on material strength and rigidity.
SO basically, the train DOES stop - but only the bit in actual contact with the bearing, a part which is totally insignificant in relation to the overall size.

 

I'm sure I saw a question somewhere among the ball bearings...

The Trumpet Major was, IIRC, one of Thomas Hardy's novels


Off topic, but I always remember the story about the editor of one of the SF magazines in the 1930's or 40's who tried to make sure no sexual references got into the stories. Of course, the authors tried their best to get past him. One author (possibly the young Asimov) decided that the plot required the presence of a "ball-bearing mouse-trap". A couple of pages later, this device was revealed to be....
...a tomcat

Tom

 

I got me a nice quote quiz for you. This is a literal quote (including the spelling mistakes) from an actual English general. All I want to know is who wrote it.

"Tis sutch rainy weather that in the trench we are up to the knees in water which is not very comfortabell espetially when wee ar to stay 24 houers in the trench beefor wee ar relived."

 

Patience young Roel, I believe quiz etiquette indicates the quiz is probably Ossian's but only once David confirms his answers.

You could always have used your quote in the "Quotes Quiz":

http://www.fun-online.sk/forum/viewtopi ... c&start=60

I'll give the answer to mine, I guess two months and no answer is enough time to wait. :lol:

 

Ossian is correct. Go ahead sir & ask the next question.

Thank you Simon. (Aren't these foreigners so rude!)

 

I will happily pass the honour to Roel -- it looks an interesting question!
I just wish some of the kids I used to teach could spell that well

Tom

 

You are quite right, the thing is though that when asked I can't come up with a quiz and when I know one I just want to ask it right away.

The Quotes Quiz is for famous quotes though. I don't expect this one to be very famous.

I edited the question by the way, the general was English, not British.

 

"Tis sutch rainy weather that in the trench we are up to the knees in water which is not very comfortabell espetially when wee ar to stay 24 houers in the trench beefor wee ar relived."

Who said this?

Hints:
- He was English
- A young Churchill served under him during this campaign.

 

Do you mean John Churchill, Duke of Marlborough, or Winston Churchill, PM?

 

Was it by any chance Sir Bindon Blood in the Malakand Campaign (mid 1890's) WSC "served" under him as an aide/hanger on, and wrote his first newspaper reports and book out of it

Tom

 

Not Sir Bindon Blood (never heard of him I'm afraid).

Ricky: that is for you to decide. Clever thinking though.