Question

A 2kg toy car traveling at 2m/s strikes a second toy car at rest. The mass of the second toy car is 3. The two stock together and move off together. What is their resultant speed?

Answer 1

Mass of first car = Initial mass (Mi) = 2 kg
Initial velocity (Vi) = 2 m/s

Mass of both cars together = Final mass (Mf) = 2 + 3 kg = 5 kg
Final Velocity (Vf) = ?

Applying law of conservation of momentum,

Mi x Vi = Mf x Vf
2 x 2 = 5 x Vf
Vf = 4/5 = 0.8 m/s