1. A 40-kg child is standing still on a 10-kg skateboard, which is also at rest. If the child walks to the right at 2m/s, what is the resulting velocity of the skateboard?
2. A 200-g air cart traveling to the right with a speed of 4 cm/s overtook and collided with a 400-g air can traveling in the same direction with a speed of 2 cm/s. If the two carts stuck together, what was their common velocity after the collision?
3. A 200-g air cart traveling to the right with a speed of 4 cm/s collided with a 400-g air cart traveling to the left with a speed of 2 cm/s. If the two carts stuck together, what was their common velocity after the collision?
4. A rotating star expands to become a red giant, increasing its average radius from one million km to 100million km without changing its mass. What happens to the velocity of a piece of this star located at the average radius?
a. It becomes 100 times faster.
b. It becomes 100 times slower.
c. It stays the same.
d. It becomes 100 million km/s.
5. A subatomic particle with an angular momentum of +2 units breaks down into two new particles, one of which has an angular momentum of -1 units. What must the angular momentum of the other particle be?
6. How many calories does a 75-kg woman use in walking up stairs to a point that is twenty m higher?
7. a. A hostess realizes that the soup she is about to serve is too hot. If there are 100g of soup, its temperature is 50 °C, and its specific heat is 0.8 cal/g°C, how many calories must be removed from the soup so that the) temperature will be a more comfortable 40°C?
b. If she would like to cool the soup by adding water (specific heat = 1 cal/g°C) at a temperature of 5°C, how much water should she add, assuming that all the heat from the soup goes into the water (and it must also end up at 40°C)?
8. The Moon has a mass of 7 x 1022 kg and is moving 3 x 104 m/s. A 2 x 1020 kg asteroid moving 6 x 106 m/s in exactly the opposite direction as the Moon (at that moment) slams into it head on. (You can assume that there are no outside forces.)
a. Would momentum be conserved in this interaction? Why or why not?
b. If momentum were conserved, what will the velocity of the Moon be afterwards?
c. Does the combined kinetic energy of the Moon and the asteroid have to be conserved? Why or why not?
9. A 30-kg child coasts down a hill on a 20-kg sled. She pushes off from the top of the hill with a velocity of 1 m/s. At the bottom of the hill, she is moving 4 m/s. If there is no heat generated when she slides down, how high is this hill?
10. A 1-kg flower pot resting on a balcony 25 m above the ground. The railing gives way and it falls to the ground. If it is going 20 m/s when it hits the ground, how much heat did it create by friction on its way down?
11. a. One kg of water is moving 2 m/s as it goes over a dam. At the base of the dam, 13m below, how fast is that water going if air friction can be neglected?
b. If the water does not go straight over the dam, but instead goes through the hydroelectric generator in the ba. se of the darn, creating 100 J of electrical potential energy in the process, how fast will it be going after it exits the power plant at the bottom?