A 20 metric ton train moves south at 40 m/s. At what speed must it travel to hav

Question

A 20 metric ton train moves south at 40 m/s. At what speed must it travel to have three times its original momentum? Answer in units of m/s. At what speed must it travel to have a momentum of 400000 kg middot m/s ? Answer in units of m/s. If there were a speed limit for this train as it traveled through a city, but not a weight limit, what mass in kilograms must be added to the train to slow it down to 30 m/s while at the same time keeping the momentum the same as in the second part? Answer in units of kg.

Explanation / Answer

a) momentum is propotional to speed

v = 3 * 40 = 120 m/s

b) p = m v

v = p / m = (400000) / (20 metric ton) * (1 metric ton / 1000)

= 20 m/s

c) p = m v, m = p / v = 400000 / 30 = 13333.3 kg

m = 13333.3 - 20000 = 6666.67 kg

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