Unformatted text preview: 9. Identical containers of H atoms (mass ~1 u) and of He atoms (mass ~4 u) are at the same temperature and pressure. a. Which – if either – contains the greater number of atoms, the container of H or the container of He? (2 pts) b. Which – if either
has the greater average kinetic energy, the H atoms or the He atoms? (2 pts) c. Which – if either – is moving faster, the H atoms or the He atoms? (2 pts) 10. Determine the pressure 10 m below the surface of a lake. (3 pts) 11. The specific heat of aluminum is about twice that of iron. Consider two blocks of equal mass, one made of aluminum and the other one made of iron, initially at the same temperature. If the same amount of heat energy is added to each, which one (if either) ends up at the higher temperature? Explain. (3 pts) Name__________________________________ 12. A 0.10 m3 block of aluminum hangs from a spring balance. a. What will the spring balance read? (3 pts) (b
d) The block is now lowered into a tank of water until it’s completely submerged. b. Find the buoyant force on the block of aluminum. (3 pts) c. What will the spring balance read now? (3 pts) 13. For exercise, an athlete lifts a sandbag that weighs 200 N from the ground to a height of 1.5 m in a time of 2.0 s. Assume the efficiency of the human body is 25%, and that she lifts the sandbag at a constant speed. a. In applying the energy equation (given at right) to the system consisting of "K + "U g + "U sp + "E th +
the box, the earth, and the athlete, which terms are positive? Which are "E chem + ... = W + Q
negative? (If any terms are zero, ignore them.) (3 pts) b. Determine the metabolic energy expended by the athlete. (5 pts) !
c. Determine her metabolic power. (3 pts) Name__________________________________ 14. A toy roller coaster gets a 2.0 kg car moving by compressing it against a 40 N/m spring constant spring and releasing it. After a short level stretch, the car ascends a 1.0 m
high hill. How far should the spring be compressed, to just get the car to reach the top of the hill? Assume that the car moves without friction on the track. (For full credit your response must include an appropriate diagram, an explicit indication of the system you are considering, a solution beginning from fundamental equations, proper units, and significant figures.) (12 points)...
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 Fall '07
 Cui
 Physics, 25%, 1000 kg, 45°, 105 Pa, 3000 kg

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