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Two Rolling Balls (Posted on 2009-11-04) Difficulty: 3 of 5
Two identical balls roll across the top of a table on parallel paths. One of the balls has to roll down into and up out of a dip in the table. The other ball rolls on the flat all the time. Which ball gets to the far side of the table first, and why?.

No Solution Yet Submitted by Brian Smith    
Rating: 3.5000 (4 votes)

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Solution re: well... | Comment 11 of 21 |
(In reply to well... by Vishal Gupta)

Ball 1, while still up at table-top level, has a certain kinetic energy and a certain potential energy. At the middle of the trough or valley, it is going horizontally again, but its potential energy is less as it is lower, so its kinetic energy must be higher, and since it's going horizontally, it is going faster.

It slows down again to its original speed when its excess kinetic energy is converted back to potential energy when it has exited the dip.

The first ball, going through the dip, arrives first.

  Posted by Charlie on 2009-11-05 18:50:22
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