Question

A 7500 kg open train car is rolling on frictionless rails at 25.0 m/s when it starts pouring rain. A few minutes later, the car's speed is 20.0 m/s. What mass of water has collected in the car?

Answer 1

Mass of rain collected will be 1875 kg

Step-by-step explanation:

We have given mass of the train
`m_i` = 7500 kg

Velocity of the car
`v_i` = 25 m/sec

After few minutes velocity of the car = 20 m/sec

From conservation of momentum we know that
`m_iv_i=m_fv_f`

So
`7500* 25=m_f* 20`

`m_f=9375kg`

`m_f` will be sum of mass of car and mass of rain collected

As mass of car is 7500 kg

So mass of rain collected = 9375 - 7500 = 1875 kg