Physics 1050 - Fall 2015 - Midterm Exam 1 - Posted Version with Solutions
Problem 1:
You are trying to open a jar of honey and find that the lid is stuck. You are twisting the lid in the opening direction, but it won't budge. To succeed in opening the lid, what must you do?
(A) You must exert a larger torque on the lid in the opening direction than the jar is exerting on the lid in the closing direction. [78.7% picked]
(B) The angular acceleration of your hand must be greater than the angular acceleration of the lid. [2.5% picked]
(C) The angular velocity of your hand must be greater than the angular velocity of the lid. [0.0% picked]
(D) You must exert a larger torque on the lid than the lid is exerting on you. [18.8% picked]
Answer: (A) You must exert a larger torque on the lid in the opening direction than the jar is exerting on the lid in the closing direction. [78.7% picked]
Why: TBA
Problem 2:
You and your friends manage to get the Ruffner Bridge (the pedestrian bridge over Emmet Street) bouncing up and down vigorously. At what point(s) during its bounce is the bridge moving fastest?
(A) When it is at equilibrium (zero net force). [80.3% picked]
(B) When it is at the top (highest altitude) of its bounce. [1.7% picked]
(C) When it is at the bottom (lowest altitude) of its bounce. [3.8% picked]
(D) Just before it reaches the bottom (lowest altitude) of its bounce. [14.2% picked]
Answer: (A) When it is at equilibrium (zero net force). [80.3% picked]
Why: TBA
Problem 3:
You are graduating and you toss your cap into the air. While the cap is not touching anything and neglecting any effects due to the air, what aspect of the cap's motion remains constant?
(A) Its torque [2.5% picked]
(B) Its momentum [8.4% picked]
(C) Its force [4.6% picked]
(D) Its angular momentum [84.5% picked]
Answer: (D) Its angular momentum [84.5% picked]
Why: TBA
Problem 4:
A shelf breaks and your entire collection of stuffed animals begins to fall simultaneously from the same height. Neglecting any effects due to the air, which of the animals reaches the floor first?
(A) The animal with the most energy reaches the floor first. [0.8% picked]
(B) The animal with the largest mass reaches the floor first. [2.1% picked]
(C) They all reach the floor simultaneously. [96.2% picked]
(D) The animal with the largest weight reaches the floor first. [0.8% picked]
Answer: (C) They all reach the floor simultaneously. [96.2% picked]
Why: TBA
Problem 5:
Your friends have made a huge batch of lemonade and they need a huge ice cube to chill it. After buying the ice cube, they tie the cube in the middle of a pickup truck's horizontal bed and begin driving home. While the truck and its contents are all moving forward horizontally at constant velocity, the ropes break so is nothing holding the ultra-slippery ice cube in place. The ice cube
(A) slides backward to the back of the pickup truck's horizontal bed. [21.8% picked]
(B) slides forward to the front of the pickup truck's horizontal bed. [1.3% picked]
(C) slides to the side of the pickup truck's horizontal bed. [0.4% picked]
(D) remains in the middle of the pickup truck's horizontal bed. [76.6% picked]
Answer: (D) remains in the middle of the pickup truck's horizontal bed. [76.6% picked]
Why: TBA
Problem 6:
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. [0.4% picked]
(B) can be greater than, less than, or equal to the water bottle's weight. [25.9% picked]
(C) is equal to the water bottle's weight. [73.6% picked]
(D) is less than the water bottle's weight. [0.0% picked]
Answer: (B) can be greater than, less than, or equal to the water bottle's weight. [25.9% picked]
Why: TBA
Problem 7:
A weight-lifting competition leaves you so exhausted that you sleep right through to the 22nd century. When you awake, you learn that your next competition is on the moon, where gravity is much weaker than on Earth. Your trainer has brought your favorite 100-kilogram bar to the moon with you. That bar
(A) still has a mass of 100 kilograms, but its weight is much less than on Earth. [97.9% picked]
(B) has a much smaller mass and a much smaller weight than on Earth. [0.0% picked]
(C) still has a mass of 100 kilograms and its weight is the same as on Earth. [0.8% picked]
(D) has a much smaller mass than on Earth, but its weight is the same as on Earth. [1.3% picked]
Answer: (A) still has a mass of 100 kilograms, but its weight is much less than on Earth. [97.9% picked]
Why: TBA
Problem 8:
Which of the following is experiencing zero net force?
(A) A sailboat that is moving in a straight line at a steady speed on a windy day. [81.6% picked]
(B) A bicycle that is turning left at a constant speed of 15 miles-per-hour. [5.9% picked]
(C) A skateboard that has just rolled off the top of a ramp and is not touching anything. [4.2% picked]
(D) A person who is bungee jumping and is exactly at the bottom (the lowest point) of their first bounce. [8.4% picked]
Answer: (A) A sailboat that is moving in a straight line at a steady speed on a windy day. [81.6% picked]
Why: TBA
Problem 9:
You throw your water bottle straight up and it rises for 2 seconds before reaching its peak height of about 20 meters (66 feet). After only 1 second of rising, what was the water bottle's approximate height?
(A) About 7.5 meters [6.3% picked]
(B) About 15 meters [72.4% picked]
(C) About 10 meters [13.0% picked]
(D) About 5 meters [8.4% picked]
Answer: (B) About 15 meters [72.4% picked]
Why: TBA
Problem 10:
Two puppies are fighting over a toy. Each puppy grips one end of that toy in its mouth and pulls. Suddenly, the puppy on the right pulls especially hard on the toy and moves its end of the toy to the right. The other puppy manages to keep its end of the toy from moving. Alas, the toy breaks and the game ends. Breaking the toy required energy and that energy was provided
(A) only by the puppy on the left. [0.8% picked]
(B) by both puppies, but most was provided by the puppy on the right. [6.3% picked]
(C) in equal amounts by the two puppies. [7.1% picked]
(D) only by the puppy on the right. [85.8% picked]
Answer: (D) only by the puppy on the right. [85.8% picked]
Why: TBA
Problem 11:
You are heading south for spring break and have boarded a plane at the local airport. The plane starts its engines and its propellers begin to spin. They spin slowly at first, then faster and faster over a period of many seconds. Why don't the propellers reach full rotational speed immediately?
(A) Each propeller has a large force that opposes the engine's force. [1.7% picked]
(B) Each propeller has a large rotational mass that resists rapid angular accelerations. [87.0% picked]
(C) Each propeller has a large torque that opposes the engine's torque. [5.4% picked]
(D) Each propeller has a large rotational mass that resists large angular velocities. [5.9% picked]
Answer: (B) Each propeller has a large rotational mass that resists rapid angular accelerations. [87.0% picked]
Why: TBA
Problem 12:
Builders obtain a vertical reference line by hanging a small but heavy object on a string beneath a fixed support point. Why does that system (object and string) settle so that the string is vertical?
(A) The downward pull of the object's weight cause the string to accelerate downward so that it becomes vertical. [4.2% picked]
(B) The system is in equilibrium only when the object's downward weight points directly away from the support point and produces zero torque on the system about its support point. [47.7% picked]
(C) Gravity pulls the object straight down and the object pulls the string taut in a vertical direction. [38.9% picked]
(D) The downward pull of the object's weight causes it to fall vertically and it pulls the string downward with it. [9.2% picked]
Answer: (B) The system is in equilibrium only when the object's downward weight points directly away from the support point and produces zero torque on the system about its support point. [47.7% picked]
Note: (C) Gravity pulls the object straight down and the object pulls the string taut in a vertical direction. [38.9% picked] is also acceptible as an answer, so credit has been given for both answers.
Why: TBA
Problem 13:
While riding on a bus, you place your backpack on the seat next to you. The bus is heading forward at a moderate speed when a child suddenly runs across the street in front of it. The driver slams on the brakes, stopping the bus in time to avoid the child, but your backpack moves forward off the seat and falls to the floor. Why didn't your backpack stay on the seat?
(A) The backpack's inertia kept it moving forward as the bus accelerated backward and slowed to a stop. [98.7% picked]
(B) The bus seat pushed the backpack forward, in the direction opposite the bus's acceleration. [0.4% picked]
(C) The bus seat pushed the backpack forward, in the direction of the bus's velocity. [0.0% picked]
(D) The backpack pushed itself forward as the bus pushed itself backward. [0.8% picked]
Answer: (A) The backpack's inertia kept it moving forward as the bus accelerated backward and slowed to a stop. [98.7% picked]
Why: TBA
Problem 14:
A hammer's weight acts in the downward direction, yet you can use the hammer to pound a nail into the ceiling. Why?
(A) The nail's downward weight is so much smaller than that of the hammer that the overall force due to gravity on the nail is upward and the nail moves upward into the ceiling. [5.4% picked]
(B) Your downward weight is so much greater than that of the hammer that the net force on the hammer is upward as it strikes the nail. [5.0% picked]
(C) The upward-moving hammer transfers its upward momentum to the nail by way of a huge upward force exerted on the nail for a short period of time. [88.7% picked]
(D) Your downward weight is so much greater than that of the nail that you dominate the hammer's motion. [0.8% picked]
Answer: (C) The upward-moving hammer transfers its upward momentum to the nail by way of a huge upward force exerted on the nail for a short period of time. [88.7% picked]
Why: TBA
Problem 15:
A melon is sitting at equilibrium in the weighing basket of a grocery store spring scale. You lift the melon upward slightly and release it. As the melon bounce up and down, the melon is accelerating upward whenever
(A) its velocity is upward. [2.5% picked]
(B) it is above equilibrium. [4.6% picked]
(C) it is below equilibrium. [90.8% picked]
(D) its velocity is downward. [2.1% picked]
Answer: (C) it is below equilibrium. [90.8% picked]
Why: TBA
Problem 16:
You are bicycling up a hill at constant velocity. Neglecting any effects do to the air, in which direction is the hill's overall force on the bicycle?
(A) Downhill [16.3% picked]
(B) Uphill [4.6% picked]
(C) Upward [77.4% picked]
(D) Forward horizontally [1.7% picked]
Answer: (C) Upward [77.4% picked]
Why: TBA
Problem 17:
A tractor is using a chain to pull a heavy log northward at constant velocity. The net force on the log
(A) points upward and northward (at an angle between the two individual directions). [1.3% picked]
(B) points downward and northward (at an angle between the two individual directions). [4.2% picked]
(C) points toward the north. [2.1% picked]
(D) is zero. [92.5% picked]
Answer: (D) is zero. [92.5% picked]
Why: TBA
Problem 18:
A skateboarder drops onto a steep ramp and begins to accelerate rapidly downhill along that ramp. What force is causing the skateboarder to accelerate downhill? [Neglect any effects due to friction or air resistance.]
(A) The downhill ramp force that is the sum of the skateboarder's weight and the support force exerted on the skateboarder by the ramp's surface [45.6% picked]
(B) The support force exerted on the ramp's surface by the skateboarder [0.0% picked]
(C) The support force exerted on the skateboarder by the ramp's surface [1.3% picked]
(D) The skateboarder's weight [53.1% picked]
Answer: (A) The downhill ramp force that is the sum of the skateboarder's weight and the support force exerted on the skateboarder by the ramp's surface [45.6% picked]
Why: TBA
Problem 19:
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) No, because the ball's momentum doesn't change between throw and catch. [22.6% picked]
(B) No, because the ball's mass doesn't change between throw and catch. [30.5% picked]
(C) Yes. [38.9% picked]
(D) No, because the ball's weight doesn't change between throw and catch. [7.9% picked]
Answer: (C) Yes. [38.9% picked]
Why: TBA
Problem 20:
You are walking a dog on a rope when the dog begins to chase a squirrel. You momentarily lose your grip and the rope begins to slide swiftly through your motionless hands. Why does your skin suddenly feel very hot?
(A) The rope is accelerating and that acceleration increases the rope's temperature. [0.4% picked]
(B) The dog is doing work on your hands and your hands are turning that work into thermal energy in your skin. [1.7% picked]
(C) The rope's inertia converts the dog's forward energy into thermal energy in your skin. [3.3% picked]
(D) The dog is doing work on the rope and sliding friction is converting the rope's energy into thermal energy in your skin and the rope's surface. [94.6% picked]
Answer: (D) The dog is doing work on the rope and sliding friction is converting the rope's energy into thermal energy in your skin and the rope's surface. [94.6% picked]
Why: TBA
Problem 21:
You are a passenger in a car that is driving on a highway. At this moment, you are feeling both your weight downward and a weight-like sensation that points toward the right. At this moment, your
(A) acceleration is toward the right. [5.4% picked]
(B) acceleration is toward the left. [86.2% picked]
(C) velocity is toward the right. [2.1% picked]
(D) velocity is toward the left. [6.3% picked]
Answer: (B) acceleration is toward the left. [86.2% picked]
Why: TBA
Problem 22:
You are weighing a melon on a spring scale. The scale reports the melon's correct weight only when
(A) the force the melon exerts on the scale is equal in amount to the force the scale exerts on the melon. [20.1% picked]
(B) the melon is motionless. [10.0% picked]
(C) the melon is in equilibrium (zero net force). [68.6% picked]
(D) the melon is accelerating at the acceleration due to gravity. [1.3% picked]
Answer: (C) the melon is in equilibrium (zero net force). [68.6% picked]
Why: TBA
Problem 23:
You stand ready to run a long race on a level track. As the race starts, you accelerate forward. What is causing you to accelerate forward?
(A) The support force that the track exerts on you. [14.6% picked]
(B) You are pushing yourself forward. [13.4% picked]
(C) The frictional force that the track exerts on you. [70.3% picked]
(D) Your mass. [1.7% picked]
Answer: (C) The frictional force that the track exerts on you. [70.3% picked]
Why: TBA
Problem 24:
You drop a baseball 3 feet onto three different rigid horizontal surfaces. One surface is motionless, the second surface is moving steadily upward, and the third surface is moving steadily downward. From which surface does the ball bounce upward highest?
(A) From the motionless surface. [9.6% picked]
(B) It bounces to the same height from all three surfaces. [11.7% picked]
(C) From the downward moving surface. [8.8% picked]
(D) From the upward moving surface. [69.9% picked]
Answer: (D) From the upward moving surface. [69.9% picked]
Why: TBA
Problem 25:
As they descend out of mountains, many highways have safety turnoffs to rescue trucks that have lost their brakes. A truck entering such a turnoff finds itself driving through deep sand on a gradually rising slope. Why is that arrangement better than simply stopping the truck promptly with a rigid, immovable barrier?
(A) The sand reverses the direction of the truck's energy. [0.8% picked]
(B) The sand removes the truck's momentum slowly with modest forces, but allows the truck to retain its energy. [19.2% picked]
(C) The sand gradually extracts much of the truck's energy, but allows the truck to retain its momentum. [6.7% picked]
(D) The sand removes the truck's momentum slowly with modest forces and gradually extracts much of the truck's energy. [73.2% picked]
Answer: (D) The sand removes the truck's momentum slowly with modest forces and gradually extracts much of the truck's energy. [73.2% picked]
Why: TBA
Problem 26:
A soccer player kicks the ball toward the goal. After the ball leaves the player's foot and neglecting any effects due to the air, the ball experiences
(A) a forward force that increases steadily as the ball approaches the goal. [1.7% picked]
(B) a forward force that decreases steadily to zero as the ball approaches the goal. [7.9% picked]
(C) a forward force that increases steadily to the midpoint between kicker and goal and then decreases steadily to zero as the ball approaches the goal. [5.0% picked]
(D) no force in the forward direction. [85.4% picked]
Answer: (D) no force in the forward direction. [85.4% picked]
Why: TBA
Problem 27:
Pedaling your bicycle provides power to its rear wheel and propels your bicycle forward. The bicycle's front wheel turns freely and rolls forward as the bicycle moves forward. What force(s) is principally responsible for the bicycle's forward acceleration as you pedal your bicycle forward from rest on a level (horizontal) road?
(A) The pavement exerts a forward frictional force on the bottom of the rear wheel. [59.0% picked]
(B) The pavement exerts forward frictional forces on the bottoms of the front and rear wheels. [27.6% picked]
(C) The pavement exerts forward support forces on the bottoms of the front and rear wheels. [5.4% picked]
(D) The pavement exerts a forward support force on the bottom of the rear wheel. [7.9% picked]
Answer: (A) The pavement exerts a forward frictional force on the bottom of the rear wheel. [59.0% picked]
Why: TBA
Problem 28:
You are working in a pizza parlor. You toss a spinning disk of pizza dough into the air. As the dough stretches outward and the flying disk becomes wider, what happens to the disk's angular velocity?
(A) It decreases. [80.8% picked]
(B) It increases. [8.8% picked]
(C) It remains constant because angular velocity is conserved. [5.9% picked]
(D) It remains constant because no torque acts on the disk. [4.6% picked]
Answer: (A) It decreases. [80.8% picked]
Why: TBA
Problem 29:
A tennis racket is strung with elastic strings that store and return collision energy very well, better than a tennis ball does. How stiff should the string surface be in order to make a tennis ball bouncing off that surface travel as fast as possible?
(A) The string surface should be relatively soft so that it dents deeply during the bounce. [37.2% picked]
(B) The string surface should be essentially rigid so that it barely dents during the bounce. [51.5% picked]
(C) The stiffness of the string surface doesn't matter because the ball is responsible for the bounce. [0.0% picked]
(D) The string surface should have the same stiffness as the ball so that they both dent the same amount during the bounce. [11.3% picked]
Answer: (A) The string surface should be relatively soft so that it dents deeply during the bounce. [37.2% picked]
Why: TBA
Problem 30:
To win a prize at the local fair, you must drop a glass marble into a glass bowl on a hard floor and that marble must come to rest in the bottom of the bowl. You try many times, but the marble keeps bouncing out of the bowl. What physics issue is preventing the marble from stopping in the bowl?
(A) The marble has too much torque to come to rest in the bowl. [0.8% picked]
(B) The marble can't do work on the bowl, so it is unable to get rid of its energy. [76.5% picked]
(C) The marble can't do an impulse on the bowl, so it is unable to get rid of its momentum. [20.2% picked]
(D) The marble has too much force to come to rest in the bowl. [2.5% picked]
Answer: (B) The marble can't do work on the bowl, so it is unable to get rid of its energy. [76.5% picked]
Why: TBA