Question

A 10,000-kg railroad car travels down the track at 30 m/s and hits a second stationary railroad car of 20,000 kg. The cars become coupled and continue traveling. Calculate the final velocity of the cars.

Answer 1

10 m/s

Step-by-step explanation:

The problem can be solved by using the law of conservation of momentum: the initial momentum has to be equal to the final momentum, so we can write the following

`p_i = p_f`

`m_1 u_1 + m_2 u_2 = (m_1 +m_2 )v`

where

`m_1 = 10,000 kg` is the mass of the first car

`u_1=30 m/s` is the initial velocity of the first car

`m_2 = 20,000 kg` is the mass of the second car

`u_2 = 0` is the initial velocity of the second car

`v` is the final velocity of the two combined cars after the collision

Re-arranging the equation and substituting the numbers, we find

`v=(m_1 u_1 +m_2 u_2)/(m_1+m_2)=((10,000)(30)-0)/(10,000+20,000)=10 m/s`