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

Answer:

Mass of rain collected will be 1875 kg

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 $7500\times 25=m_f\times 20$

$m_f=9375kg$

$m_f$ 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