Problem 1:
Why does a beanbag bounce poorly when dropped on a concrete sidewalk and bounce well when dropped on a trampoline?
Answer: (B) 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. [46.3% picked]
Why: Video Discussion
Problem 2:
You are at the gym, exercising on a step machine. You have one foot on each of the machine's pedals and you move those pedals up and down as you step. The pedals always push upward on your feet, but they push harder while moving downward than while moving upward. When during this exercise is your foot transferring energy to the pedal that it is touching?
Answer: (C) As that pedal moves downward. [90.7% picked]
Why: Video Discussion
Problem 3:
As you run up the marble steps of the Supreme Court building to begin arguing your case, your right foot skids to a stop on one of the steps. During that skid, what work is being done by your right foot and the step?
Answer: (C) The step does negative work on your foot and your foot does zero work on the step. [84.6% picked]
Why: Video Discussion
Problem 4:
Your shopping cart contains a bag of groceries and you are pushing that cart up a straight ramp at a steady speed. In what direction is the shopping cart's force on that bag of groceries?
Answer: (A) The cart is pushing the bag directly upward. [85.8% picked]
Why: Video Discussion
Problem 5:
You are trying to weigh a huge tomato you grew in your garden, but your spring scale has lost the needle on its dial. You can successfully weigh your tomato, using the dial-less spring scale, but you will also need a calculator, a 1-pound bag of sugar, and
Answer: (D) a ruler. [88.2% picked]
Why: Video Discussion
Problem 6:
You drop a tennis ball from rest onto a rigid, motionless granite counter. The ball bounces straight upward and peaks at 50% of its original height. Before you let it drop, the ball had gravitational potential energy due to its height above the counter. What has become of that gravitational potential energy at the moment the ball reaches peak height on its rebound?
Answer: (A) 50% is now gravitational potential energy in the ball and 50% is thermal energy in the ball. [48.4% picked]
Why: Video Discussion
Problem 7:
To win a stuffed animal at the state fair, you simply need to drop a glass marble onto a stationary glass plate and have the marble come to rest on that plate. Unfortunately, when the marble hits the plate, it bounces upward because the marble
Answer: (A) retains essentially all of its energy but transfers a large amount of momentum to the plate. [93.1% picked]
Why: Video Discussion
Problem 8:
You drop a beanbag (a bag full of beans) onto four different surfaces: a hard floor, another beanbag, a feather pillow, and a foam pillow. The floor is the hardest surface, the feather pillow is the softest surface. The beanbag bounces upward the least from the second beanbag and it bounces upward most from the foam pillow. To which surface does the beanbag transfer the most momentum during its bounce?
Answer: (A) To the foam pillow. [53.3% picked]
Why: Video Discussion
Problem 9:
A rabbit runs by and your dog begins to pull hard on her leash. Despite your best efforts, both of you begin to accelerate toward the rabbit. Compare the amount of force that the dog exerts on the leash to the amount of force the leash exerts on the dog.
Answer: (C) The two forces are equal in amount. [88.2% picked]
Why: Video Discussion
Problem 10:
You are using a string to lift a heavy picnic basket up to your treehouse. Alas, the string isn't strong enough for the job. The picnic basket becomes motionless, even though you are moving the portion of string you are holding upward, and the string breaks. Breaking the string required energy and that energy was provided by
Answer: (B) you. [79.3% picked]
Why: Video Discussion
Problem 11:
You are riding a train that is moving straight ahead at high speed. The train comes to a curve in the tracks and begins to turn toward the left. You find yourself pressed against the right side of your seat. What force, if any, is pushing you toward the right?
Answer: (B) There is no force pushing you toward the right. [78.0% picked]
Why: Video Discussion
Problem 12:
A player has tossed a lacrosse ball to a distant teammate and that ball is in the air, exactly midway between the two players. Neglecting any effects due to the air itself, what net force is the ball experiencing?
Answer: (D) A net force pointing directly downward. [72.8% picked]
Why: Video Discussion
Problem 13:
A large mobile (a sculpture supported by a single cord) hangs from the ceiling of an art museum. Since the cord supports the mobile at its center of gravity and mass, that the mobile is balanced and experiences zero net torque. The mobile is
Answer: (C) moving with constant angular momentum, which may be zero. [77.2% picked]
Why: Video Discussion
Problem 14:
Two coins, a quarter and a dime, roll off a level table side-by-side at the same time and in the same direction. The coins soon hit the level floor below the table. The two coins were traveling at the same horizontal speed when they left the table. In this situation,
Answer: (A) the quarter hits the floor at approximately the same time as the dime and the quarter hits at approximately the same distance from the table as does the dime. [90.2% picked]
Why: Video Discussion
Problem 15:
You toss your lucky nickel directly upward and watch it rise to its peak height. At the moment that nickel reaches that peak height, its velocity is
Answer: (C) zero and its acceleration is downward. [93.9% picked]
Why: Video Discussion
Problem 16:
A driver in heavy traffic is texting and accidently collides with the stopped car in front of her. Her car and everything in it suddenly come to a complete stop. The passengers in the rear seat are stopped by their seat belts and shoulder straps, which stretch as they stop the passengers. As compared to rigid restraints, stretchable belts and straps remove the same momentum from each passenger, but they transfer that momentum using
Answer: (C) a smaller force for a longer time. [82.1% picked]
Why: Video Discussion
Problem 17:
You're at the lake and watch two children jump off a dock at the same time. They both kick equally hard during their jumps, but one child jumps mostly upward while the other child jumps mostly forward. After they leave the dock,
Answer: (D) the child who jumps forward reaches the water before the child who jumps upward. [87.0% picked]
Why: Video Discussion
Problem 18:
You have a cart attached to your bicycle and two children are sitting motionless in that cart at the bottom of a hill. You bicycle up to the top of the hill via the gradual path and stop so that the three of you can enjoy the view. You then bicycle down the hill via a steep path and return to exactly where you started and are motionless again. What overall work did you and the bicycle do on the cart and children during the roundtrip?
Answer: (B) Zero overall work. [70.7% picked]
Why: Video Discussion
Problem 19:
A high school pitcher can throw a 50 mile-per-hour fastball, but it takes a phenomenal professional pitcher to throw a 100 mile-per-hour fastball. Compared to the 50 mile-per-hour fastball, the 100 mile-per-hour fastball carries
Answer: (A) 4 times as much kinetic energy. [74.4% picked]
Why: Video Discussion
Problem 20:
A pickup truck is stopped at a red light and you are standing in the back of that truck, wearing rollerskates. The light turns green and the truck heads forward. Why do you roll out the back of the truck?
Answer: (D) Inertia. [96.7% picked]
Why: Video Discussion
Problem 21:
You're making pizza for a dinner party and you toss a spinning disk of dough into the air to stretch it outward. While nothing is touching the disk, what aspect of the disk is constant? [neglect effects due to air]
Answer: (A) Its angular momentum is constant. [83.7% picked]
Why: Video Discussion
Problem 22:
You take a toboggan (a flat-bottom vehicle for sliding down slippery hills) to the top of an icy hill. Before sliding down the hill, however, you connect a long spring from the toboggan to a tree part way down the slope on the left. When you get on the toboggan and it begins to move frictionlessly on the hill's surface, how does the toboggan move?
Answer: (C) It accelerates in the direction that reduces its total potential energy as quickly as possible. [53.7% picked]
Why: Video Discussion
Problem 23:
When you are riding a pogo stick, you are basically bouncing on a spring. When you stand motionless on the pogo stick, the spring compresses to become 1 inch shorter than its equilibrium length. Suppose you are riding the pogo stick and, at this moment, its spring is 2 inches shorter than its equilibrium length. At this moment,
Answer: (B) you are accelerating upward. [72.8% picked]
Why: Video Discussion
Problem 24:
Before its launch, the Mars rover Curiosity had a mass of 899 kilograms and it weighed 1982 pounds. After landing on Mars, Curiousity's mass
Answer: (A) remains unchanged, but its weight is different. [99.6% picked]
Why: Video Discussion
Problem 25:
You are carrying an unopned 10-pound bag of chocolate chips as you ride your skateboard at constant velocity along a horizontal road. While you hold up the bag at a constant height, you are doing
Answer: (A) zero work on the bag and it is doing zero work on you. [91.1% picked]
Why: Video Discussion
Problem 26:
You stand atop a vertical cliff, with the ocean about 80 meters (260 feet) below you. You throw a heavy rock horizontally off the cliff and it falls for 4 seconds before splashing into the water at a point about 20 meters (65 feet) from the base of the cliff. 2 seconds after the rock left your hand, approximately where is the rock located?
Answer: (A) 60 meters above the ocean and about 10 meters horizontally from the cliff. [55.7% picked]
Why: Video Discussion
Problem 27:
Your little nephew is visiting and is having fun diving onto your bed. He leaps off your dresser and begins to fall toward the bed's surface. At what moment does he reach peak downward speed?
Answer: (B) At the moment he reaches equilibrium on the bed for the first time. [56.1% picked]
Why: Video Discussion
Problem 28:
A xylophone is a musical instrument consisting of metal bars that you strike with a ball on the end of stick. As the ball bounces from a bar, that bar begins to emit a musical tone. The instrument gently supports the bar at two special points along the bar's length. Suppose you remove the bar from the instrument and strike the bar at one of those special points. Why does the bar emit almost no sound?
Answer: (D) Since the bar's vibrational nodes do not move during the bar's vibration, striking one of those nodes won't cause that vibration. [71.1% picked]
Why: Video Discussion
Problem 29:
A girl who is skating straight across perfectly slippery ice picks up a hockey puck that was resting motionless on the ice. As a result of acquiring that hockey puck, the girl
Answer: (A) slows down because her initial momentum is now distributed over more mass. [93.9% picked]
Why: Video Discussion
Problem 30:
You're having trouble loosening a rusty bolt with a small wrench, so you borrow a large wrench from your neighbor. Exerting only a modest force on the handle of this new wrench easily unscrews the bolt. The large wrench helps because it
Answer: (D) allows you to exert your force far from the center of rotation, so that you produce a large torque on the bolt. [89.8% picked]
Why: Video Discussion