Energy and Momentum Quiz True or False

1. A 3000 kg hot air balloon is rising at a speed of 5 m/s. How fast does it rise after the pilot jettisons five 20 kg sandbags? -> 5.17 m/s
2. Baron von Sinister has tied Dolly Damsel to the train tracks and cut the brake lines on the local 3:10 express. The train consists of an engine, hopper car, and caboose, totaling 10,000 kg. As soon as the engineer sees Dolly tied to the tracks 80 m away he cuts the engine—but the train is still traveling at 25 m/s with only friction to slow it down (the coefficient of friction of the train's steel wheels on the steel rails is 0.3). Luckily the train is rolling through a supply depot. After 50 m of travel the conductor is able to load another 5,000 kg of coal into the hopper instantaneously. How far will the train travel in total from the moment the engineer turns off the engine? Is Dolly saved?

-> 98.6 m; Baron von Sinister's dastardly plan succeeds
3. One of the major differences between a rifle and a pistol is the longer barrel of a rifle, which enables expanding gas from the gun's burning propellant to exert a force on the bullet for a longer period time, increasing the bullet's momentum and therefore its range. If a rifle fired from the shoulder (1.5 m off the ground) exerts a force of 9000 N on a 50 g bullet for 10 ms before it leaves the rifle's barrel, what is the maximum range of the bullet?

-> 7,470 m
4. How far away from Earth is the center of mass between the earth (6.0 × 1024 kg) and the moon (7.3 × 1022 kg)? The earth and moon are 384,000 km apart. -> 4615 km
5. A cue ball (0.17 kg) traveling at 4 m/s collides elastically with the stationary eight ball (0.16 kg). How fast will the cue ball be traveling after the collision? Will it be traveling in the same direction as before the collision, or will it reverse direction? -> 0.12 m/s, same direction
6. When dropped from a height of 1 m onto a hard floor, a standard golf ball will rebound 0.6 m into the air. What is the coefficient of restitution of the golf ball? -> 0.77
7. One way in which bullet velocities are measured is a device called a ballistic pendulum. It consists of a block of wood suspended from the ceiling by wire. When a bullet (mass m) is fired at the block (mass M), it collides and embeds itself into the wood. If the center of mass of the bullet/block combination swings up a height h, how fast was the bullet going when it entered the block?

->
8. A fire hose can be used to break down the wall of a burning building by sending 500 liters of water per minute shooting out of the nozzle at 5 m/s. What is the average force felt by the wall while the hose is on? The density of water is 1 kg/L. -> 8.33 N
9. A model rocket's engines can make 50 N of thrust. How long would they need to fire for in order to launch a 4 kg rocket 500 m into the air? -> 5.6 s
10. A horse jockey (50 kg) and a sumo wrestler (150 kg) stand on opposite ends of a 5 m long balance beam that weighs 300 kg. If the jockey and sumo both take a 1 m step towards the center of the beam, how far does the center of mass of the system move?


-> 0.2 m

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