A 50 kg pitcher throws a baseball with a mass of 0.15 kg. If the ball is thrown with a positive velocity of 35 m/s and there is no net force on the system, what is the velocity of the pitcher?

The pitcher and ball start at rest, so their total momentum is zero. After the throw, conservation of momentum gives (0.15 kg)(35 m/s) + (50 kg)v = 0, so v = −5.25/50 = −0.105 m/s. Rounded to the nearest tenth, the pitcher’s velocity is −0.1 m/s, choice A.

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