Question

A 4000 kg freight car moving at 3 km/hr collides and couples with an 8000 kg freight car which is initially at rest. the final speed of the combined cars is

Answer 1

Answer: 0.28 m/s (1 km/hr)

Step-by-step explanation:

This is an inelastic conservation of momentum question.

First, convert the speed to m/s: 3 km/hr (1000m/1km)(1hr/3600s) = .83 m/s

Then, Momentum before = Momentum after;

Momentum before = m1v1 + m2v2 = 4000(.83) + 8000(0)

Momentum after: (m1 + m2)v3 → (4000 + 8000)v3

Set these equal: 4000(.83) = 12000v3 and solve to get: v3=.28 m/s :)