Question

Train A is moving North at 12 m/s and has a mass of 2000 kg.Train B is moving South at 8 m/s and has a mass of 4000 kg. Ifthe two trains collide and stick to each other, how fast dothey move after the collision, and in what direction?

Answer 1

Mass A = 2000 kg

velocity A = 12 m/s (North)

Mass B= 4000 kg

Velocity B= -8 m/s (South)

We adopt that North is positive and South is negative.

Conservation of momentum (p)

• Pi = Pf

• ma * va + mb*vb = (ma+mb) Vf

Where Vf is the final velocity after the collision.

Replacing:

(2000* 12 ) + (4000*-8)= (2000+4000) vf

24,000- 32,000 = 6,000 vf

-8,000 = 6,000 vf

-8,000 / 6,000 = vf

vf = -1.3334 m/s

vf = 1.3334 m/s , South