engine has a mass M = 40,000 kg travelling in speed v = 25m/s. Strikes a car of
ID: 2024856 • Letter: E
Question
engine has a mass M = 40,000 kg travelling in speed v = 25m/s. Strikes a car of mass m = 4000 kg initially at rest. after the collision they together. What were the initial momentum and kinetic energy of the engine? What was the momentum of the engine-car combination as they moved away from the collision? What was their speed immediately after the collision? What physical principle did you use to find these? What was the kinetic energy of the engine-car combination immediately after the collision? Was kinetic energy conserved? Was momentum conserved? What impulse was delivered to the car by the engine? If the collision time was t = 3 times 10-2 s, what was the average force exerted by the truck on the car?Explanation / Answer
a. the engine had an initial momentum p=mv is 60,000 x 25 = 1,500,000 kgm/s, and kinetic energy KE=1/2mv2 is 1/2 x 60,000 x 25 x 25 = 1.875 x 107 J.
b.i) since the car was at rest, the car-train momentum is the same as the train's initial momentum, 1,500,000 kgm/s.
ii) Their speed is p/m 1,500,000 / 66,000 = 22.7 m/s.
iii) We used Conservation of Momentum.
c. i) the kinetic energy KE=1/2mv2 is 1/2 x 66,000 x 22.72 = 1.7 x 107 J.
ii) no, kinetic energy was not conserved.
iii) yes, momentum was conserved.
d. the impulse mv delivered to the car was 6,000 x 22.7 = 136,200 Ns. the average force exerted p/t was 136,200 / 3 x 10-2 = 4.54 x 106 N.
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