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Unformatted text preview: x ( t ) =  gt 2 + v t How fast will the bullet be traveling when it comes back down and hits the earth? To answer this we must (i) solve for the time at which the bullet will hit the earth, and (ii) find the velocity function, so that we can evaluate it at that time. Setting x ( t ) = 0 again and solving for t we find that either t = 0 or t = 2 v / g . Well, t = 0 is just the time when the bullet left the ground, so the time at which it will come back, falling from above, must be t = 2 v / g . Using our knowledge from the previous section, v ( t ) =  gt + v . If we plug in t = 2 v / g , we find that the velocity of the bullet as it comes back down and hits the ground is  g (2 v / g ) + v =  v . In other words, the bullet is traveling at the same speed it had when it was just fired, only in the opposite direction....
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 Fall '10
 DavidJudd
 Physics, Acceleration

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