# Basic physics, solve for speed?

by mhb22079
Tags: basic, physics, solve, speed
 Emeritus Sci Advisor PF Gold P: 4,980 this is a conservation of momentum question where the initial momemtum must be equal to the final momentum. The initial momentum is clearly: $$p_i = m_b v_bi$$ The momentum immediately after impact must be equivalent to this: $$p_f = m_a v_a + m_b v_bf = p_i = m_b v_bi$$ The only problem I can see is working out the velocity soon after impact. Is there any other data supplied with this question or not? If not just make an estimate of the deceleration of car a and work backwards from the distance moved.