Physics 1050 - Fall 2015 - Midterm Exam 2 - Posted Version with Solutions
Problem 1:
A water bottle is touching the top of a table. The downward force the water bottle exerts on the table
(A) is greater than the water bottle's weight. [1.7% picked]
(B) is less than the water bottle's weight. [1.3% picked]
(C) is equal to the water bottle's weight. [57.0% picked]
(D) can be greater than, less than, or equal to the water bottle's weight. [40.1% picked]
Answer: (D) can be greater than, less than, or equal to the water bottle's weight. [40.1% picked]
Problem 2:
Because of bad planning during the design and construction of a high-rise apartment building, all 50 floors of the building receive their water from a single pipe. That pipe is fed from a water tank located on the building's roof. On opening day, residents on various floors begin taking showers and have different experiences. They quickly discover that the total energy per liter in the spraying water is (neglecting any effects of viscosity and friction)
(A) the same on all floors, but the speed of the spraying water is greater on higher floors. [20.7% picked]
(B) greater on higher floors. [5.1% picked]
(C) the same on all floors, but the speed of the spraying water is smaller on higher floors. [60.3% picked]
(D) smaller on higher floors [13.9% picked]
Answer: (C) the same on all floors, but the speed of the spraying water is smaller on higher floors. [60.3% picked]
Problem 3:
All objects in our universe exert gravitational forces on one another. The Earth exerts a gravitational force on the moon and the moon exerts a gravitational force on the Earth. Compare those two gravitational forces.
(A) The Earth's gravitational force on the moon is smaller in amount than the moon's gravitational force on the Earth. [2.5% picked]
(B) The Earth's gravitational force on the moon is greater in amount than the moon's gravitational force on the Earth. [43.6% picked]
(C) The Earth's gravitational force on the moon is equal to the moon's gravitational force on the Earth. [5.1% picked]
(D) The Earth's gravitational force on the moon is equal in amount but opposite in direction to the moon's gravitational force on the Earth. [48.7% picked]
Answer: (D) The Earth's gravitational force on the moon is equal in amount but opposite in direction to the moon's gravitational force on the Earth. [48.7% picked]
Problem 4:
An astronaut is orbiting the Earth inside the International Space Station and he is hovering in the middle of the cabin. The net force on that astronaut is
(A) equal to his weight and he is accelerating downward (toward the center of the Earth). [65.7% picked]
(B) zero, but his acceleration is changing as his path bends around the Earth. [11.0% picked]
(C) zero, but his velocity is changing as his path bends around the Earth. [11.0% picked]
(D) zero and he is not accelerating. [12.3% picked]
Answer: (A) equal to his weight and he is accelerating downward (toward the center of the Earth). [65.7% picked]
Problem 5:
A block of wood floats motionless on a calm lake. Part of the block is in water and part of it is in air. When the sun goes down, the air grows colder and its density increases. The block of wood
(A) becomes heavier, but it continues to float exactly as it did before the air became colder. [1.7% picked]
(B) moves downward so that more of the block is in water and less of the block is in air. [38.8% picked]
(C) moves upward so that more of the block is in air and less of the block is in water. [59.1% picked]
(D) becomes lighter, but it continues to float exactly as it did before the air became colder. [0.4% picked]
Answer: (C) moves upward so that more of the block is in air and less of the block is in water. [59.1% picked]
Problem 6:
You are trying to set the world's record for drinking water through the tallest drinking straw. What could you do to have the best chance of setting this record?
(A) Choose a good-weather day when the atmospheric pressure is as large as possible. [79.7% picked]
(B) Use the widest drinking straw you can fit in your mouth. [2.1% picked]
(C) Choose a bad-weather day when the atmospheric pressure is as small as possible. [13.5% picked]
(D) Use the narrowest drinking straw you can find. [4.6% picked]
Answer: (A) Choose a good-weather day when the atmospheric pressure is as large as possible. [79.7% picked]
Problem 7:
Why does a beanbag bounce poorly when dropped on a concrete sidewalk and bounce well when dropped on a trampoline?
(A) During their collision, the beanbag transfers much less momentum to the soft trampoline than to the hard sidewalk. The beanbag's remaining momentum causes the beanbag to bounce upward from the trampoline. [5.5% picked]
(B) Hard surfaces do not store and return energy well, so objects do not bounce well from hard concrete sidewalks. Soft surfaces store and return energy efficiently, so objects bounce well from soft trampolines. [10.1% picked]
(C) During their collision, the beanbag transfers much less energy to the soft trampoline than to the hard sidewalk. The beanbag's remaining energy causes the beanbag to bounce upward from the trampoline. [3.4% picked]
(D) When the beanbag collides with the hard sidewalk, the beanbag is softer, and receives and wastes nearly all of the collision energy. When the beanbag collides with the soft trampoline, the trampoline is softer, and receives and returns nearly all of the collision energy. [81.0% picked]
Answer: (D) When the beanbag collides with the hard sidewalk, the beanbag is softer, and receives and wastes nearly all of the collision energy. When the beanbag collides with the soft trampoline, the trampoline is softer, and receives and returns nearly all of the collision energy. [81.0% picked]
Problem 8:
To catch a football successfully, you should allow the ball to push your hands in the direction of its travel. Allowing your hands to move with the football is crucial because it allows you to
(A) extract momentum from the football. [48.5% picked]
(B) add energy to the football. [2.5% picked]
(C) add momentum to the football. [6.3% picked]
(D) extract energy from the football. [42.6% picked]
Answer: (D) extract energy from the football. [42.6% picked]
Problem 9:
If a golf ball had no dimples and were smooth instead, it would
(A) keep its forward momentum longer and travel farther. [4.6% picked]
(B) lose forward momentum more quickly and travel less far. [94.1% picked]
(C) lose forward momentum more quickly, but travel equally far. [1.3% picked]
(D) keep its forward momentum longer, but travel equally far. [0.0% picked]
Answer: (B) lose forward momentum more quickly and travel less far. [94.1% picked]
Problem 10:
You are driving forward in a sports car with the windows closed. A squirrel runs across the road and you slam on the brakes. As the car slows to a stop, missing the squirrel, the air pressure inside the car is
(A) the same near the front of the car as near the back of the car. [24.9% picked]
(B) higher near the front of the car than near the back of the car. [58.2% picked]
(C) zero. [1.7% picked]
(D) lower near the front of the car than near the back of the car. [15.2% picked]
Answer: (B) higher near the front of the car than near the back of the car. [58.2% picked]
Problem 11:
When you catch a ball that was thrown to you by a teammate, that ball exerts a force on your hand. Can the force that the ball exerts on your hand be larger than the force your teammate exerted on the ball when throwing it?
(A) Yes. [46.0% picked]
(B) No, because the ball's momentum doesn't change between throw and catch. [18.6% picked]
(C) No, because the ball's weight doesn't change between throw and catch. [9.3% picked]
(D) No, because the ball's mass doesn't change between throw and catch. [26.2% picked]
Answer: (A) Yes. [46.0% picked]
Problem 12:
Newton's first law states that an object that is free of external forces moves at constant velocity. The conservation of momentum is responsible for that law (and the concept of inertia) because an object that is
(A) free of external forces turns its momentum into energy at a constant rate and therefore moves at constant velocity. [10.5% picked]
(B) moving at constant momentum converts that momentum into a constant force, so it moves at constant velocity. [1.7% picked]
(C) free of external forces cannot change its momentum and since it can't change its mass, it can't change its velocity. [78.1% picked]
(D) moving at constant velocity carries a constant amount of force with it as part of its momentum. [9.7% picked]
Answer: (C) free of external forces cannot change its momentum and since it can't change its mass, it can't change its velocity. [78.1% picked]
Problem 13:
Water distribution systems often include water towers that are located well above all the rest of the plumbing. In addition to storing water, what is the purpose of the water tower?
(A) The tower also stores force. [0.0% picked]
(B) The tower also stores energy. [53.6% picked]
(C) The tower also stores momentum. [0.4% picked]
(D) The tower also stores pressure. [46.0% picked]
Answer: (B) The tower also stores energy. [53.6% picked]
Problem 14:
When running in a 400-meter race, the runners complete one trip around a track. As the runners sprint around the curved ends of that track, they lean inward—their upper bodies tilt toward the inside or center of the curve. If a runner remained upright while sprinting around the curve, what would happen? [neglect air effects]
(A) The runner would accelerate outward—away from the inside or center of the curve. [7.2% picked]
(B) The runner's upper body would not accelerate inward fast enough to stay above the runner's feet and the runner would tip over. [88.2% picked]
(C) The runner would travel at constant velocity, despite an inward frictional force on the runner's feet. [0.4% picked]
(D) The runner would accelerate forward, despite an inward frictional force on the runner's feet. [4.2% picked]
Answer: (B) The runner's upper body would not accelerate inward fast enough to stay above the runner's feet and the runner would tip over. [88.2% picked]
Problem 15:
A can of sugar soda and a can of diet soda have the same volume, but sugar soda has a greater density than diet soda. If you put both cans in a pool of water, the can of diet soda will float to the surface while the can of sugar soda will sink to the bottom. Why?
(A) The two cans experience equal buoyant forces, but the can of diet soda weighs less than the water is displaces while the can of sugar soda weighs more than the water it displaces. [78.9% picked]
(B) The can of diet soda experiences a larger buoyant force than the can of sugar soda. [18.6% picked]
(C) The can of diet soda displaces more water than the can of sugar soda. [2.5% picked]
(D) The two can drew straws to see which one would float and the can of diet soda won. [0.0% picked]
Answer: (A) The two cans experience equal buoyant forces, but the can of diet soda weighs less than the water is displaces while the can of sugar soda weighs more than the water it displaces. [78.9% picked]
Problem 16:
A kicked soccer ball that is not spinning moves forward through air that had been motionless. Just after the ball has passed by, in which direction is the air's average velocity?
(A) Backward—opposite the direction of the ball's velocity. [18.2% picked]
(B) Forward—in the direction of the ball's velocity. [64.4% picked]
(C) Downward. [14.8% picked]
(D) Upward. [2.5% picked]
Answer: (B) Forward—in the direction of the ball's velocity. [64.4% picked]
Problem 17:
You are riding a roller coaster and are going through a loop-the-loop. At the top of the loop, you and your car are inverted, but you feel pressed into your seat. In which direction, if any, are you accelerating?
(A) upward (toward the sky) [6.3% picked]
(B) forward (horizontally in the direction the car is moving) [3.4% picked]
(C) downward (toward the ground) [89.0% picked]
(D) backward (horizontally opposite the direction the car is moving) [1.3% picked]
Answer: (C) downward (toward the ground) [89.0% picked]
Problem 18:
A wooden ball floats motionless in a glass of water so that exactly half the ball is beneath the water's surface. Salad oil is about 10% less dense than water. If you place the same wooden ball in salad oil, the ball will
(A) float motionless with exactly half the ball beneath the oil's surface. [1.7% picked]
(B) float motionless with less than half the ball beneath the oil's surface. [20.3% picked]
(C) float motionless with more than half the ball beneath the oil's surface. [72.2% picked]
(D) sink to the bottom of the oil. [5.9% picked]
Answer: (C) float motionless with more than half the ball beneath the oil's surface. [72.2% picked]
Problem 19:
You are roller skating around a circular track at a steady speed. Are you accelerating and, if so, in which direction?
(A) You are accelerating inward, toward the center of the circular track. [72.2% picked]
(B) You are accelerating outward, away from the center of the circular track. [5.9% picked]
(C) You are accelerating forward, in the direction of your velocity. [3.8% picked]
(D) You are not accelerating. [18.1% picked]
Answer: (A) You are accelerating inward, toward the center of the circular track. [72.2% picked]
Problem 20:
At a baseball game, a pitcher throws a fastball toward the catcher. When the ball is half way to home plate and no one is touching it, where on the ball is the air pressure highest?
(A) At the front of the ball—the side nearest home plate. [78.4% picked]
(B) At the top of the ball. [6.4% picked]
(C) At the back of the ball—the side nearest the pitcher. [11.4% picked]
(D) At the bottom of the ball. [3.8% picked]
Answer: (A) At the front of the ball—the side nearest home plate. [78.4% picked]
Problem 21:
Firefighters are battling a fire on the 10th floor of a building. Their truck draws water from a fire hydrant, pressurizes it with a pump, and delivers it to a hose with a nozzle. When sprayed upward from ground level, the water only reaches the 8th floor. To get the water to reach the fire, what must the firefighters do? [Ignore viscosity and assume the water is in steady state flow after the pump.]
(A) Use a second pump to increase the pressure of water entering their hose. [88.6% picked]
(B) Raise the hose so that its nozzle sprays water upward from the 4th floor. [4.2% picked]
(C) Raise the hose so that its nozzle sprays water sideways from the 10th floor. [5.1% picked]
(D) Raise the hose so that its nozzle sprays water upward from the 8th floor. [2.1% picked]
Answer: (A) Use a second pump to increase the pressure of water entering their hose. [88.6% picked]
Problem 22:
A Super Soaker is a popular toy that sprays a powerful stream of water from a nozzle connected to a pressurized tank in the toy. Suppose you are wearing roller skates (to eliminate friction) and suddenly begin to spray water from your Super Soaker at a friend directly north of you. How and when will you accelerate?
(A) You will accelerate southward and you will begin accelerating when the water begins to spray out of your Super Soaker. [88.2% picked]
(B) You will not accelerate because the force you exert on the water cancels the force the water exerts on you. [2.5% picked]
(C) You will not accelerate because the water is not hitting you and you are therefore experiencing zero net force. [1.7% picked]
(D) You will accelerate southward and you will begin accelerating when the water begins to hit your friend. [7.6% picked]
Answer: (A) You will accelerate southward and you will begin accelerating when the water begins to spray out of your Super Soaker. [88.2% picked]
Problem 23:
You are at an amusement park and are about to try the drop tower. It lifts you high in the air and then lets you fall freely for about 2 seconds. As you fall, your apparent weight is zero and you feel weightless because
(A) you experience an upward feeling of acceleration that exactly cancels your feeling of weight. [73.0% picked]
(B) your weight becomes zero as you fall. [0.8% picked]
(C) you are traveling downward and your downward velocity exactly cancels your feeling of weight. [22.4% picked]
(D) you are accelerating upward and your upward acceleration exactly cancels your feeling of weight. [3.8% picked]
Answer: (A) you experience an upward feeling of acceleration that exactly cancels your feeling of weight. [73.0% picked]
Problem 24:
You are visiting Machu Picchu in Peru, an Inca ruin located almost 8000 feet (2400 meters) above sea level. As you explore the site, some of your fellow tourists experience altitude sickness. Although the air's temperature is fine and it's perfectly breathable, something about the air is causing trouble from some people. How does high altitude air differ from sea level air when both have the same temperature?
(A) The high altitude air has a lower pressure than the sea level air, but their densities are equal. [27.4% picked]
(B) The high altitude air has a lower pressure and lower density than the sea level air. [65.8% picked]
(C) The high altitude air has a smaller average thermal kinetic energy per particle than the sea level air. [0.0% picked]
(D) The high altitude air has a lower density than the sea level air, but their pressures are equal. [6.8% picked]
Answer: (B) The high altitude air has a lower pressure and lower density than the sea level air. [65.8% picked]
Problem 25:
A tennis ball is often hit with topspin (its top surface moves forward as it spins), so that it deflects the passing air upward. How does this ball move?
(A) It accelerates upward. [3.8% picked]
(B) It does not accelerate vertically. [0.4% picked]
(C) It accelerates downward faster than it would if it were simply falling. [81.0% picked]
(D) It accelerates downward more slowly than it would if it were simply falling. [14.8% picked]
Answer: (C) It accelerates downward faster than it would if it were simply falling. [81.0% picked]
Problem 26:
A spaceship is traveling in a circular orbit about 100 miles above Earth's atmosphere. With the ship pointing forward (in the direction of its velocity), it fires its rocket engine. The plume of rocket exhaust travels backward (opposite the direction of the ship's velocity). What happens to the ship's orbit?
(A) The ship follows the same circular orbit, but it moves faster and therefore completes each orbit in less time than before. [24.5% picked]
(B) The ship orbits exactly as before. There is no atmosphere on which the rocket can push, so it is unable to alter its orbit. [5.1% picked]
(C) The ship now follows an elliptical orbit and its average altitude above Earth's atmosphere is greater than before. [68.8% picked]
(D) The ship now follows an elliptical orbit and its average altitude above Earth's atmosphere is less than before. [1.7% picked]
Answer: (C) The ship now follows an elliptical orbit and its average altitude above Earth's atmosphere is greater than before. [68.8% picked]
Problem 27:
You're filming a movie and you arrange for two unoccupied cars to drive horizontally off a tall cliff side-by-side at the same velocity. The Mercedes sedan weighs twice as much as the Mini Cooper. In this situation, the two cars hit the level ground below the cliff at approximately
(A) the same distance from the cliff, but the Mercedes sedan hits much sooner than the Mini Cooper. [1.7% picked]
(B) the same time and at the same distance from the cliff. [76.8% picked]
(C) the same time, but the Mercedes sedan hits considerably farther from the cliff than the Mini Cooper. [3.0% picked]
(D) the same time, but the Mini Cooper hits considerably farther from the cliff than the Mercedes sedan. [18.6% picked]
Answer: (B) the same time and at the same distance from the cliff. [76.8% picked]
Problem 28:
A bicycle touches the ground at only two points, forming a base of support that is a line. As the bicycle (including the rider) moves forward, it steers itself automatically so that it
(A) maintains constant velocity. [0.8% picked]
(B) turns steadily either to the left or to the right. [4.2% picked]
(C) does not accelerate horizontally. [3.4% picked]
(D) tends to put its base of support below its center of gravity, thereby returning the bicycle to its unstable equilibrium after any minor tip. [91.6% picked]
Answer: (D) tends to put its base of support below its center of gravity, thereby returning the bicycle to its unstable equilibrium after any minor tip. [91.6% picked]
Problem 29:
Air flows around a horizontal bend in a large metal heating duct (pipe). The diameter of the duct itself is constant. Neglecting any effects due to viscosity or turbulence, where in that duct is the air pressure greatest?
(A) At the start of the bend. [1.3% picked]
(B) On the inside of the bend—nearest to the center of the curve. [6.3% picked]
(C) On the outside of the bend—farthest from the center of the curve. [92.4% picked]
(D) At the finish of the bend. [0.0% picked]
Answer: (C) On the outside of the bend—farthest from the center of the curve. [92.4% picked]
Problem 30:
You are pulling a wagon forward on a level sidewalk and the wagon is experiencing no other horizontal force. As you exert your forward force on the wagon, the wagon exerts a backward force on you. When do those two forces cancel so that the wagon does not accelerate?
(A) When you and the wagon have equal velocities. [10.5% picked]
(B) When those two forces are equal in amount but opposite in direction so that they sum to zero. [76.8% picked]
(C) When you and the wagon have equal masses. [1.3% picked]
(D) They never cancel because they act on different objects. [11.4% picked]
Answer: (D) They never cancel because they act on different objects. [11.4% picked]
Video Discussion