Download 45 Questions on How Things Work with Answers - Exam 2 | PHYS 140 and more Exams Classical Physics in PDF only on Docsity!
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1. A #2 pencil
2. One scantron answer sheet
3. One exam question booklet
Instructions— This is a closed book exam. You have sixty (60) minutes to complete it.
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- A Physics 140 student has a weight of 500 N. She is standing on a scale in an elevator that is accelerating upward at 1 m/s^2. What does the scale read?
a. 1000 N b. 500 N c. 450 N d. 550 N
- On a cool day, you are driving your car with the windows rolled up. Up ahead, you see a car on the side of the road that is on fire and totally engulfed in flames. Since the fire department is on the scene, you drive past the car without reducing your speed. As you get near the car on fire, you feel warmth on your face, which immediately subsides when you are past the burning car. How was the heat transferred from the burning car to your face?
a. convection b. radiation c. conduction d. black body
- Sublimation is the phase transition from
a. liquid to gas. b. solid to liquid. c. gas to solid. d. solid to gas.
- Soil heats up much faster than water when the two are exposed to sunlight. Use that fact and your understanding of heat transfer to predict which way the wind will blow near the surface of the earth as the sun sets near the seashore.
a. The surface wind will blow from the land toward the water. b. The surface wind will blow alternately back and forth along the shore, parallel to the boundary between land and water. It will reverse directions every few minutes. c. The surface wind will blow steadily in one direction along the shore, parallel to the boundary between land and water. d. The surface wind will blow from the water toward the land.
- You add a little hot tea to ice water at 0°C; the mixture will remain at 0°C so long as some ice remains. Where does the tea’s extra thermal energy go?
a. It goes into the ice’s latent heat of melting. b. It goes into ice’s latent heat of vaporization. c. It goes into raising the temperature of a small amount of the liquid water, but not the ice. d. It goes into the liquid water’s latent heat of vaporization.
2 of 10 pages
- You are riding a multi-speed bicycle up a steep hill that's 100 m high and want to do as little work as possible on your way up the hill.
a. Your choice of gears doesn't matter because you'll do the same amount of work climbing the hill no matter which gear you choose. b. You should choose the largest crank sprocket (attached to the pedals) and the smallest freewheel sprocket (attached to the rear wheel). c. You should choose the smallest crank sprocket (attached to the pedals) and the largest freewheel sprocket (attached to the rear wheel). d. You should choose the largest crank sprocket (attached to the pedals) and the largest freewheel sprocket (attached to the rear wheel).
- A 1 kg ball dropped from a height of 4 m rebounds only to 2 m after hitting the ground. So its starting potential energy is about 40 Joules. The amount of energy converted to heat is about (Remember: g = 10 m/s^2 and 1 Joule = 1 kg m^2 /s^2 )
a. 2 Joules. b. 10 Joules. c. 20 Joules. d. 40 Joules.
- The surface of the moon is exposed to full solar radiation because it has no atmosphere. Some of the solar radiation is reflected, some is absorbed. Why then does the moon not heat up endlessly until it disintegrates?
a. Convection in the soil carries energy away. b. Its temperature rises until it is able to radiate heat away into space as fast as it arrives from the sun. c. It has disintegrated but the light just hasn’t reached us yet. d. Because the moon is isolated from the sun by empty space, the sun's heat can't reach it (only light can) and the moon doesn’t experience any changes in temperature.
- Some travel mugs taper outward at the bottom so that they have very wide bases. Why does this shape make such a mug particularly stable and keep it from flipping over during the morning commute?
a. The mug’s wide base allows for a greater gyroscopic effect, preventing the mug from tipping over. b. The mug’s wide base gives it an unstable equilibrium that is able to counteract the motion of the car. c. The mug’s wide base requires a larger support force which keeps the mug from tipping over. d. The mug’s wide base ensures that its total potential energy will continue to increase as it tips, so it will naturally return to its stable equilibrium.
- Your dryer is broken, so you have to hang your wet clothes from the washing machine outside to dry. Under which conditions would your clothes dry fastest?
a. When it is 50°F with 50% relative humidity. b. When it is 75°F with 50% relative humidity. c. They will dry at the same rate at any temperature with 50% relative humidity. d. The clothes will not dry with 50% relative humidity.
4 of 10 pages
- Why does burned gasoline do more work on the piston of an automobile engine during the power stroke than the piston does on the unburned fuel-air mixture during the compression stroke?
a. The pressure is much higher in the burned gas than in the unburned fuel-air mixture. b. The pressure is much lower in the burned gas than in the unburned fuel-air mixture. c. By the 2nd^ law of thermodynamics, the burned gas must do the same amount of work on the piston as the piston does on the unburned fuel-air mixture. d. Since there is an additional frictional force, no work is done on the fuel or the piston.
- One blackbody emits most of its radiation in the infrared region of the electromagnetic spectrum. If most of the radiation of another blackbody is emitted in form of visible light, its emitted power would be ______ and its temperature would be ______.
a. lower, higher b. lower, lower c. higher, higher d. higher; lower
- Solid nitrogen has a greater density than liquid nitrogen. You put a block of solid nitrogen into a container of liquid nitrogen. What happens?
a. The solid nitrogen floats in the liquid nitrogen. b. The liquid nitrogen sublimes. c. The solid nitrogen sinks in the liquid nitrogen. d. The liquid nitrogen boils.
- In Discovery Room 5, you held an air-filled balloon in liquid nitrogen. What happened to the air in the balloon?
a. It expanded. b. It contracted. c. It remained at a constant volume. d. It remained at a constant temperature.
- You place three nonflammable objects in a fire. They are identical in shape and size, but one object is black, the second is white, and the third is shiny silver. After a few minutes, all three objects are at the same temperature: 1800° C. They remain solid and are now glowing with thermal radiation. Which one is glowing most brightly?
a. The first object (black). b. They are all glowing with equal brightness. c. The third object (silver). d. The second object (white).
5 of 10 pages
- Which is true about steam at 100° C versus water at 100° C?
a. Steam at 100° C contains more energy per kilogram than water at 100° C. b. Water at 100° C contains more energy per kilogram steam at 100° C. c. They both contain the same amount of energy per kilogram. d. Water only contains more energy per kilogram than steam on the Kelvin temperature scale.
- You take two objects in your hand. The first one is in wood and feels warmer than the other one, which is metal. Which of the two objects has a higher temperature?
a. the metal object b. the wood object c. they are at the same temperature d. not enough information to tell
- Suppose you have a gas which gives up heat energy as it does work on its surroundings. Must the temperature of the gas increase, decrease or can you not determine how the temperature will behave?
a. Increase b. Decrease c. Stay the same. d. Cannot tell from the information provided.
- You are riding on a playground swing. As you swing backward, your speed decreases until you are at the highest point, when you momentarily come to rest. At the moment when you are at rest, you are
a. accelerating forward. b. not accelerating at all. c. accelerating backward. d. accelerating upward. e. accelerating downward.
- A ball bounces off the wall and is observed to be travelling at a speed of 5 m/s. The coefficient of restitution between the ball and the wall is known to be 0.25. How fast was the ball travelling prior to the collision?
a. 5 m/s b. 20 m/s c. 2.5 m/s. d. 1.25 m/s. e. 10 m/s.
7 of 10 pages
- What does a spring scale measure?
a. The force applied by the spring. b. The mass of the object. c. The acceleration of the object. d. The strength of gravity.
- In Discovery Room 4, you dropped a basketball with a small ball on top. After the collision, the small ball went higher than the height it was initially dropped from. How did this happen?
a. In the collision between the two balls, some of the basketball’s energy was transferred to the small ball. b. The coefficient of restitution of the ball is greater than one. c. Energy moves from the floor into both balls. d. Energy is not conserved in this collision.
- When you drop a rubber ball on the floor and it bounces, the direction of its velocity reverses because
a. the ball’s inertia keeps it traveling in a straight line, but in the opposite direction. b. the ball's momentum is conserved. c. the ball's energy is conserved. d. the floor exerts an upward support force on the ball and this force stops the ball's descent and eventually propels it upward.
- You are driving your car and you turn right around the corner while keeping a constant speed of 15mph. What is the direction of your apparent acceleration?
a. forward b. right c. left d. backward.
- As you ride on a merry-go-round, you feel a strong outward pull that feels just like the force of gravity. This feeling of acceleration occurs because
a. your velocity is toward the center of the merry-go-round and you experience a feeling of acceleration in the direction opposite your velocity. b. you are accelerating away from the center of the merry-go-round and experience a feeling of acceleration in the direction of your acceleration. c. you are accelerating toward the center of the merry-go-round and experience a feeling of acceleration in the direction opposite your acceleration. d. your velocity is away from the center of the merry-go-round and you experience a feeling of acceleration in the direction of your velocity.
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- You drink out of a plastic soft drink bottle in a warm car and empty it. When you are done, you screw on the cap tightly and throw the bottle on the floor. The next morning, after a freezing night, the car is very cold. What do you observe about the bottle?
a. It is unchanged. b. It is shriveled up, since cold air has lower pressure. c. It is shriveled up, since cold air has less density. d. It is shriveled up, since cold air has greater density.
- Why can you see your breath on a cold day?
a. When it is cold, water vapor can absorb latent heat and condense. b. Lower temperature favors high relative humidity and favors condensation. c. Lower temperature favors low relative humidity and condensation. d. Cold temperatures make the water vapor in your breath less dense and easier to see.
- If you blow on your hand with your mouth wide open, then you feel the warmth of your breath. If you pucker your lips and blow, your breath is
a. warmer because air expanding. b. warmer because air is contracting. c. cooler because air is expanding. d. cooler because air is contracting.
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