Answer
The magnitude of the velocity is 0.870 m/s, and they are moving to the right.
Work Step by Step
We can use conservation of momentum to solve this question. Let's assume that the right is the positive direction.
$p_2 = p_1$
$(m_A+m_B)~v_2 = m_A~v_{A1}+ m_B~v_{B1}$
$v_2 = \frac{m_A~v_{A1}+ m_B~v_{B1}}{m_A+m_B}$
$v_2 = \frac{(70.0~kg)(4.00~m/s)+(65.0~kg)(-2.50~m/s)}{135.0~kg}$
$v_2 = 0.870~m/s$
The magnitude of the velocity is 0.870 m/s, and they are moving to the right.
