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A freight car, open at the top, weighing 1.50 tons, is coasting along a level track with negligible friction at 3.30 ft/s when
it begins to rain hard. The raindrops fall vertically with respect to the ground. What is the speed (in feet/second)
of the car when it has collected 0.600 tons of rain?
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Let me start with my notices along the text (to make it more clear).
1. The car moves on horizontal track.
2. Its initial mass is 1500 kilograms.
3. Its mass steadily increases due to rain.
4. The rain do not add "the momentum" to the car.
The "momentum conservation law" is/says
= .
= 1500 kg, = 3.30 ft/s, = 1500 + 600 = 2100 kg.
Substitute this data into the equation and find the unknown speed under the question.
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The lesson to learn from this solution:
The "momentum conservation law" for the body with changing/varying mass.