Question

A 1000 kg car and a 1500 kg car are driving in opposite directions at 20 m/s and 10 m/s respectively. If the cars collide head-on and stick together, determine their combined speed after the collision.

Answer 1

Hi there!

Recall the conservation of momentum for an inelastic collision:

$\large\boxed{m_1v_1 + m_2v_2 = (m_1 + m_2)v_f}}$

Remember, velocity is a VECTOR and direction must be accounted for. Let the 1000 kg car have a positive velocity and the 1500 kg car have a negative velocity (opposite direction).

Plug in the given values:

$(1000)(20) + (1500)(-10) = (1000 + 1500)v_f}}$

Solve:

$20000 -15000 = 2500v_f}}\\\\5000 = 2500v_f\\\\v_f =\boxed{ 2 m/s}$