Answer to Spare Me, Sally!

    Sally spares no effort in pinning down this line of bowling. So far, her dog is one up on her! 

    Sally is a power bowler; her 5-kg ball has a velocity of 8 m/s when it strikes the 2-kg pin head on. After the collision, the ball's velocity is 4 m/s. 

     Since you know that total momentum is conserved, you should be able to easily calculate the velocity of the pin after the collision!

Before the collision, only the bowling ball has momentum: 
     (5 kg)(8 m/s) = 40 kg-m/s
The total momentum after the collision must still be 40 kg-m/s. Since the ball's final momentum is 
     (5 kg)(4 m/s) = 20 kg-m/s, the remaining 20 kg-m/s is the pin's. So,
     (20 kg-m/s) / (2 kg) = 10 m/s
 
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