Question

A freight car with a mass of 10 metric tons is rolling at 108 km/h along a level track when it collides with another freight car, which is initially at rest. If the speed of the cars after they couple together is 36 km/h, what is the mass of the second car?

Question options:

40 metric tons

20 metric tons

10 metric tons

5 metric tons (Incorrect answer)

Answer 1

Answer: 20 metric tons

Explanation: i got it right

Answer 2

m = 20 metric ton

Step-by-step explanation:

Given,

The mass of the freight car, M = 10,000 kg

The velocity of the car before the collision, U = 105 km/h

The mass of another freight car, m = ?

The velocity of another freight car before the collision, u = 0 km/h

The velocity of the coupled car after the collision, V = 36 km/h

According to the conservation of momentum

MU + mu = MV + mV

mV = MU - MV ∵ mu = 0

m = M(U - V)/V

= 10,000 (108 - 36) / 36

= 20,000 kg

Hence, the mass of the another freight car is, m = 20,000 kg