PHY 119 Practice Exam 3 Solutions
Circle the correct answer in each of the following multiple choice questions. (5 points each)
1. What is true about an airfoil for a plane in flight? a
(a) The air pressure above the airfoil is lower than below.
(b) The air pressure above the airfoil is greater than below.
(c) The air speed above the airfoil is slower than below.
(d) The air speed is the same above and below the airfoil.
2. Which of the following isn’t a consequence of the second law of thermodynamics? c
(a) Heat flows spontaneously only from hot to cold objects.
(b) There is no heat engine with perfect efficiency.
(c) Condensation occurs when relative humidity is above 100%
(d) There is no refrigeration cycle with an infinite coefficient of performance.
3. How much greater is an object’s radiative power if its temperature is increased from 310 K
to 400 K? b
(a) 1.290 times
(b) 2.772 times
(c) 0.775 times
(d) 1.665 times
4. During each cycle, a heat engine receives releases 3300 J of thermal energy into a cold reservoir
each cycle, while producing 5000 J of work. What is the efficiency of this heat engine? b
(a) 0.66
(b) 0.60
(c) 0.40
(d) 1.52
5. Why is fiberglass such a good choice for stuffing walls? d
(a) Glass itself is a great thermal insulator against conduction.
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, (b) Fiberglass is a very strong material, so it helps support the structure of your home.
(c) Its sharp edges help deter rodents from entering the walls of your home.
(d) By preventing convection, fiberglass utilizes the low thermal conductivity of air to in-
sulate homes.
6. How much energy does it take to increase the temperature of 0.12 kg of water from 24˝ C to
53˝ C? a
(a) 14560 J
(b) 9457 J
(c) 11946 J
(d) 26381 J
7. An ice cube is given to you in a room-temperature room. Your goal is to prevent it from
melting. Out of the following, which is the best course of action? b
(a) Place the ice cube in a metal container.
(b) Place the ice cube in a Styrofoam container.
(c) Place the ice cube near a window, where there is a lot of sunlight.
(d) Place the ice cube in front of a fan, and turn the fan on its highest setting.
8. Which of the following is appropriately classified as heat (as opposed to work)? d
(a) Lifting a heavy object with a pulley.
(b) Using the wind to move a sailboat.
(c) Plugging in an electrical appliance into an outlet.
(d) Rubbing your hands together.
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Circle the correct answer in each of the following multiple choice questions. (5 points each)
1. What is true about an airfoil for a plane in flight? a
(a) The air pressure above the airfoil is lower than below.
(b) The air pressure above the airfoil is greater than below.
(c) The air speed above the airfoil is slower than below.
(d) The air speed is the same above and below the airfoil.
2. Which of the following isn’t a consequence of the second law of thermodynamics? c
(a) Heat flows spontaneously only from hot to cold objects.
(b) There is no heat engine with perfect efficiency.
(c) Condensation occurs when relative humidity is above 100%
(d) There is no refrigeration cycle with an infinite coefficient of performance.
3. How much greater is an object’s radiative power if its temperature is increased from 310 K
to 400 K? b
(a) 1.290 times
(b) 2.772 times
(c) 0.775 times
(d) 1.665 times
4. During each cycle, a heat engine receives releases 3300 J of thermal energy into a cold reservoir
each cycle, while producing 5000 J of work. What is the efficiency of this heat engine? b
(a) 0.66
(b) 0.60
(c) 0.40
(d) 1.52
5. Why is fiberglass such a good choice for stuffing walls? d
(a) Glass itself is a great thermal insulator against conduction.
61
, (b) Fiberglass is a very strong material, so it helps support the structure of your home.
(c) Its sharp edges help deter rodents from entering the walls of your home.
(d) By preventing convection, fiberglass utilizes the low thermal conductivity of air to in-
sulate homes.
6. How much energy does it take to increase the temperature of 0.12 kg of water from 24˝ C to
53˝ C? a
(a) 14560 J
(b) 9457 J
(c) 11946 J
(d) 26381 J
7. An ice cube is given to you in a room-temperature room. Your goal is to prevent it from
melting. Out of the following, which is the best course of action? b
(a) Place the ice cube in a metal container.
(b) Place the ice cube in a Styrofoam container.
(c) Place the ice cube near a window, where there is a lot of sunlight.
(d) Place the ice cube in front of a fan, and turn the fan on its highest setting.
8. Which of the following is appropriately classified as heat (as opposed to work)? d
(a) Lifting a heavy object with a pulley.
(b) Using the wind to move a sailboat.
(c) Plugging in an electrical appliance into an outlet.
(d) Rubbing your hands together.
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