Correct Answer to Question 13

Let A move in the +x direction. Then v_Ax = +21 m/s and v_Bx = 0.

v_CMx = (m_A * v_Ax + m_B * v_Bx)/(m_A + m_B)

v_CMx = (2 kg * 21 m/s + 0)/7 kg = 6 m/s

Velocity (x-component) of A relative to the center of mass is

v_A,CM = v_A - V_CM = 21 m/s - 6 m/s = 15 m/s

Velocity (x-component) of B relative to the center of mass is

v_B,CM = v_B - V_CM = 0 m/s - 6 m/s = -6 m/s

15 m/s, -6 m/s: Answer is C

Formula Sheet

Question 13

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