Answer:
10.0 kg
Explanation:
The problem can be solved by applying the law of conservation of momentum - the total momentum before the collision must be equal to the total momentum after the collision:
[tex]p_i = p_f\\m_A u_A + m_B u_B = m_A v_A + m_B v_B[/tex]
where:
[tex]m_A = 5.0 kg[/tex] is the mass of ball A
[tex]u_A = +20 m/s[/tex] is the velocity of ball A before the collision
[tex]m_B = ?[/tex] is the mass of ball B
[tex]u_B = +10 m/s[/tex] is the velocity of ball B before the collision (same sign of uA, since they are moving in same direction)
[tex]v_A = +10 m/s[/tex] is the velocity of ball A after collision
[tex]v_B = +15 m/s[/tex] is the velocity of ball B after collision
Re-arranging the equation, we can solve to find mB, the mass of ball B:
[tex]m_B u_B - m_B v_B = m_A v_A - m_A u_A\\m_B = \frac{m_A (v_A -u_A)}{u_B -v_B}=\frac{(5.0 kg)(10 m/s-20 m/s)}{10 m/s-15 m/s}=10.0 kg[/tex]
