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Ball and Train

Science brain teasers require understanding of the physical or biological world and the laws that govern it.

 

Puzzle ID:#2575
Fun:*** (2.2)
Difficulty:* (1.03)
Category:Science
Submitted By:204_blaze_41****

 

 

 



You're on a train that's moving forward at 50 mph. You throw a ball in the direction that the train is moving. Relative to you and the train, the ball leaves your hand travelling at 20 mph.

From the point of view of someone standing alongside the tracks, how fast is the ball moving?




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Comments

electronjohn*us*
Nov 12, 2002

That was so easy I had to read it four time looking for the trick. Here is another one for those that love this one: A boy weighing 50 pounds picks up a 20 pound rock and gets on a scale. How much does the scale read?
Give up?
70 pounds!!!! Wow, mind blowing stuff.
Phily
Dec 17, 2002

okay electronjohn, here's one for you: a 50 pound boy in a glass elevator goes to pick up a 20 lb rock, but the elevator is accelerating downwards at 16ft/s^2 and he sees a ball thrown upwards at 15m/s from 20m below him, if he started started from rest at the same time the ball was thrown, how high in relation to him will the ball be in 2 secs? oh, and how much will the rock weight?
electronjohn*us*
Feb 13, 2003

The ball will have hit the bottom of the elevator before the 2 sec. are up, so it will be a foot or two below the kid unless it bounces off the bottom of the elevator in which case we need to know more about the underside surface of the elevator and what material the ball is made of. Also the rock should wiegh 10 lbs during the elevators acceloration downward.
jimbo*au*
Nov 14, 2003

That is OK according to Newtonian mechanics but relativity tells us that there will be a tiny (almost negligible) difference due to the different frames of reference. Now if the train was travelling at 100 000 miles/sec and the ball was thrown forward at 90 000 miles per second, what speed would teh observer see the ball now?
jetdjc15
Aug 28, 2004

great teaser the ball will actually appear faster to the observer then the person who threw it........
calmsaviorAus*
Feb 14, 2007

If the ball was a ______, there would be no difference. Fill in the blank.

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