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  1. #1 Physics question - 
    Forum Ph.D. verzen's Avatar
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    I've been trying all day to understand this physics question but can't for some reason..

    The kinetic energy of a rolling billiard ball is given by . Suppose a 0.17- billiard ball is rolling down a pool table with an initial speed of 4.5 . As it travels, it loses some of its energy as heat. The ball slows down to 4.0 and then collides straight-on with a second billiard ball of equal mass. The first billiard ball completely stops and the second one rolls away with a velocity of 4.0 . Assume the first billiard ball is the system

    I got the heat lost. But how do I get the work? I tried (1/2*.17*4.0^2) - (1.2*.17*4.5^2) but that was not the correct answer for work done...


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    Quote Originally Posted by verzen View Post
    I've been trying all day to understand this physics question but can't for some reason..

    The kinetic energy of a rolling billiard ball is given by . Suppose a 0.17- billiard ball is rolling down a pool table with an initial speed of 4.5 . As it travels, it loses some of its energy as heat. The ball slows down to 4.0 and then collides straight-on with a second billiard ball of equal mass. The first billiard ball completely stops and the second one rolls away with a velocity of 4.0 . Assume the first billiard ball is the system

    I got the heat lost. But how do I get the work? I tried (1/2*.17*4.0^2) - (1.2*.17*4.5^2) but that was not the correct answer for work done...
    The problem statement is not clear. If you are looking for the work done by the frictional force in slowing down the ball before the collision, then your expression is correct (but note that you are subtracting a larger number from a smaller number so it will be a negative number). If you want the work done by the first ball on the second ball during the collision, then that is (1/2)*.17*4.0^2.


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