How fast is her racket moving immediately after the impact?

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The discussion revolves around calculating the speed of a tennis racket immediately after impact with a tennis ball using the conservation of momentum. A player swings a 1000 g racket at 10.00 m/s and hits a 60 g ball approaching at 20.0 m/s, which rebounds at 40.0 m/s. The initial calculations suggest the racket's speed post-impact should be 8.8 m/s, but there is confusion as the expected result is 6.4 m/s. Participants emphasize the importance of correctly assigning the signs of the velocities in the momentum equation. Clarifying these signs is crucial for achieving the correct final speed of the racket.
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A tennis player swings her 1000 g racket with a speed of 10.00 . She hits a 60 g tennis ball that was approaching her at a speed of 20.0 . The ball rebounds at 40.0 .

How fast is her racket moving immediately after the impact? You can ignore the interaction of the racket with her hand for the brief duration of the collision.

I used the conservation of momentum equation below

M1(Vf)1+M2(Vf)2=M1(Vi)1+M2(Vi)2

after rearranging this for Vf1 which in this case is the final speed of the racket I get 8.8m/s.

I should get 6.4m/s. Can someone please help me with this.
 
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You have to get the signs of the velocities right.
 

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