Question

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?

−0.1 m/s
−0.2 m/s
−0.7 m/s
−1.4 m/s

Answer 1

Use conservation of momentum. Initially momentum is zero, so

0 = m_ball v_ball + m_pitcher v_pitcher
v_pitcher = −(m_ball v_ball) / m_pitcher = −(0.15·35)/50 = −0.105 ≈ −0.1 m/s.

Answer: −0.1 m/s.