Consider an open railroad car rolling horizontally without friction in the midst
ID: 2250829 • Letter: C
Question
Consider an open railroad car rolling horizontally without friction in the midst of a vertically falling downpour. An appreciable amount of rain pools in the car. How will the accumulated water affect i) the linear momentum of the car? ii) the speed of the car? iii) the kinetic energy of the car? If there is loss or gain, where is it found? Be precise The train engineer now opens a drain plug at the bottom of the car, allowing water to to drain out. The car is still in motion during that time. How will the draining of the water affect i) the speed of the car? ii) the momentum of the car? iii) the kinetic energy of the car? Consider an open railroad car rolling horizontally without friction in the midst of a vertically falling downpour. An appreciable amount of rain pools in the car. How will the accumulated water affect i) the linear momentum of the car? ii) the speed of the car? iii) the kinetic energy of the car? If there is loss or gain, where is it found? Be precise The train engineer now opens a drain plug at the bottom of the car, allowing water to to drain out. The car is still in motion during that time. How will the draining of the water affect i) the speed of the car? ii) the momentum of the car? iii) the kinetic energy of the car?Explanation / Answer
Since the accumulating rainwater needs to be accelerated to stay in the car, its speed will decrease. It will lose as much momentum due to reduced speed as it gains in increased mass, so the momentum will stay the same. But since KE is proportional to the square of velocity, it will decrease.
2nd part
Since the leaving rainwater accelrate the car when it leaves, its speed will increase. It will gain as much momentum due to increased speed as it loose in decreased mass, so the momentum will stay the same. But since KE is proportional to the square of velocity, it will increase.