Question

A 7000 kg open train car is rolling on frictionlessrails at 24.5 m/s when it starts pouring rain. A fewminutes later, the car's speed is 20.0 m/s. What was the mass of the water collected in the car

Answer 1

We will have the following:

The information we have:

*Mass of the car: 7 000 kg.

*Mass of water: ?

*Initial velocity of the car: 24.5 m/s.

*Final velocity of the car: 20.0 m/s.

Now, using the conservation of momentum we will have the following:

$7000kg\cdot24.5m/s=20.0m/s(7000kg+m_w)$$\Rightarrow171500kg\cdot m/s=20m/s(7000kg+m_w)\Rightarrow7000kg+m_w=\frac{171500kg\cdot m/s}{20m/s}$$\Rightarrow m_w=8575kg-7000kg\Rightarrow m_w=1575kg$

So, the mass of water collected in the car is 1575 kg.