two objects collide and stick together,
Do you expect vf to be greater than v1 or less than v1? Explain why.

Question

two objects collide and stick together,
Do you expect vf to be greater than v1 or less than v1? Explain why.

anonymous · Answer

When two objects collide and stick together, we have a perfectly inelastic collision. In this type, energy is not conserved, but momentum always is. Therefore, $$m_1 v_1 + m_2 v_2 = (m_1 + m_2) v_f$$$$v_f = {m_1 v_1 + m_2 v_2 \over m_1 + m_2}$$If the second mass is at rest before the collision, what can be observe about the final velocity?

anonymous · Answer

Why did you guess that? 

If $v_2 = 0$, the expression for $v_f$ becomes$$v_f = {m_1 v_1 \over m_1 + m_2}$$$m_1+m_2 \gt m_1$ therefore, $v_f \lt v_1$. Assuming $m_2$ is at rest before the collision.