Problem 1:
A car traveling at 60 mph veers off the road and hits a tree. The car immediately comes to a complete stop. Fortunately, the airbag inflates and the driver comes to a stop in the airbag instead of coming to a stop on the steering wheel. Hitting the airbag rather than the steering wheel saves the driver's life because the driver
Answer: (C) transfers all of her momentum to whatever stops her, but that transfer is slower and involves a smaller force when she hits the airbag. [97.4% picked]
Why: Video Discussion
Problem 2:
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
Answer: (C) it is below equilibrium. [80.1% picked]
Why: Video Discussion
Problem 3:
You have landed a job assembling cheap furniture for a budget hotel chain. Unfortunately, the pieces don't fit together well and you have to pound them together with a 1-kg mallet. You want the 1-kg mallet that exerts the most force on the furniture, so as to overwhelm any resisting forces in the ill-fitting pieces, and that transfers the most momentum to those pieces, so as to complete the assembly with the fewest mallet blows. To achieve these goals, the part of the mallet that hits the furniture should be
Answer: (C) stiff and bouncy. [81.4% picked]
Why: Video Discussion
Problem 4:
Alice and Bob are carrying 50 pound bags of seeds from the sidewalk to your penthouse garden, 100 feet above the sidewalk. Alice carries bags up the stairs. Bob carries bags up a vertical ladder. Compare the work each person does on a bag while moving it from the sidewalk to the garden. [Neglect friction and air resistance, and assume that bags are motionless at the start and finish.]
Answer: (B) Alice and Bob do the same work on a bag. [94.4% picked]
Why: Video Discussion
Problem 5:
You make a sharp left turn in your car and your cell phone slips off the dashboard and out the right passenger window. The cell phone exited the car because
Answer: (A) the car did not exert enough leftward force on the phone to make the phone accelerate with the car. [48.1% picked]
Why: Video Discussion
Problem 6:
An acrobatic bicyclist rides a ramp and zooms through the sky for several seconds. He does a few amazing stunts on the bicycle before landing back on the ground. While he and his bicycle are not touching the ground and neglecting any effects due to the air, the one aspect of their motion that is constant is their total
Answer: (B) angular momentum. [78.4% picked]
Why: Video Discussion
Problem 7:
The plastic step you use in an exercise class bends downward 1.0 centimeter when you stand motionless on its top. When a person twice your weight stands on that same step, it bends downward approximately
Answer: (B) 2.0 centimeters. [93.1% picked]
Why: Video Discussion
Problem 8:
You're driving along a level road and approach a red light. You press the brake pedal and the car slows to a stop. As you stop, what happens to the car's forward momentum?
Answer: (B) It is transferred to the ground by way of friction forces. [62.3% picked]
Why: Video Discussion
Problem 9:
When a box skids to a stop on a motionless table, what work is done by those two objects?
Answer: (C) The table does negative work on the box. [74.0% picked]
Why: Video Discussion
Problem 10:
You are watching a tennis match and the server has just hit the ball toward her opponent on the other side of the court. Neglect any effects due to the air. Once the tennis ball has left the server's tennis racket and is traveling forward, the ball experiences
Answer: (D) no horizontal force in the forward direction. [90.9% picked]
Why: Video Discussion
Problem 11:
Your favorite marble rolls off the deck and falls for 2 seconds before hitting the ground. After only 1 second of falling, the marble was
Answer: (C) much closer to the deck than to the ground. [74.0% picked]
Why: Video Discussion
Problem 12:
Two children with different weights are riding on a seesaw. Why does having the lighter child sit farther from the pivot allow that child to balance the heavier child so that seesaw rotates properly?
Answer: (B) The farther a child sits from the pivot, the more torque that child's weight produces on the seesaw. [88.3% picked]
Why: Video Discussion
Problem 13:
You jump while standing on a bathroom scale and the scale briefly reads more than your actual weight. During that moment, the scale is exerting an upward force on you that is
Answer: (B) greater than your weight and you are accelerating upward. [91.8% picked]
Why: Video Discussion
Problem 14:
Your friend is sitting still on a playground merry-go-round and it is spinning at a steady pace (neglect friction and air resistance). You give a motionless bowling ball to your friend so that the ball suddenly starts spinning with the merry-go-round. As the ball begins to move with the merry-go-round, the merry-go-round's
Answer: (D) angular velocity decreases. [64.5% picked]
Why: Video Discussion
Problem 15:
You are riding a rollercoaster with a loop-the-loop. As you pass through the top of that loop and are upside down, you remain pressed into your seat. You are accelerating
Answer: (C) downward at more than the acceleration due to gravity. [26.8% picked]
Why: Video Discussion
Problem 16:
You are walking at constant velocity along a horizontal sidewalk, wearing a heavy backpack. You are doing
Answer: (B) zero work on the backpack and it is doing zero work on you. [80.1% picked]
Why: Video Discussion
Problem 17:
You and your friends are having a snowball fight. There are two identical snowballs approaching you, one traveling at 2 feet per second and one traveling 10 feet per second. You wisely try to avoid the faster snowball because it is carrying
Answer: (D) 25 times as much kinetic energy as the slower snowball. [68.4% picked]
Why: Video Discussion
Problem 18:
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?
Answer: (A) It decreases. [69.7% picked]
Why: Video Discussion
Problem 19:
To win a big stuffed animal at the local fair, you must toss a bouncy ball so that it comes to rest in a shallow ceramic bowl. But each time your ball lands on the bowl, the ball bounces and falls to the floor. This game is difficult to win because when the ball hits the bowl, the ball
Answer: (D) transfers much momentum but almost zero energy to the bowl. [88.3% picked]
Why: Video Discussion
Problem 20:
You are riding cable car from a valley to a mountaintop and are traveling toward the mountaintop at a steady pace. In which direction is the cable car pushing you?
Answer: (A) Directly upward. [78.8% picked]
Why: Video Discussion
Problem 21:
Your Frisbee is caught in a tree, so you have just thrown a small pebble and a large rock at the Frisbee. The two stones are halfway to their target and now have the same speed and the same direction of travel. Why should you expect the large rock to be more effective at knocking the Frisbee out of the tree than the small pebble?
Answer: (A) The large rock is carrying more momentum than the small pebble. [75.8% picked]
Why: Video Discussion
Problem 22:
You are rollerblading on ramps at the skate park. As you try steeper and steeper ramps, you find that
Answer: (D) your acceleration becomes greater. [37.7% picked]
Why: Video Discussion
Problem 23:
You jump off a porch onto a trampoline and bounce nicely. During your trip, you accelerate downward until the moment when you
Answer: (C) reach equilibrium in the trampoline (you dent the trampoline enough that it supports your weight). [82.7% picked]
Why: Video Discussion
Problem 24:
A flat-bed truck is trying to deliver a huge load of ice. The driver is in a hurry and steps hard on the accelerator. As the truck leaps forward, the ice slips off the back of the truck bed and falls to the ground. What caused the ice to leave the truck's bed?
Answer: (C) The ice's inertia kept it at approximately constant velocity as the truck accelerated out from under the ice. [97.4% picked]
Why: Video Discussion
Problem 25:
You are involved in a game of tug-o-war with a plastic clothesline. The two teams are pulling at opposite ends of the cord and each team is trying to drag the other team across a line marked on the ground. After a few minutes without progress, your team suddenly pulls the rope toward you especially hard. The opposing team has anticipated this action and is able to keep their end of the rope from moving. Your end of the rope stretches toward you and the rope breaks. Breaking the rope required energy and that energy was provided by
Answer: (A) your team. [87.9% picked]
Why: Video Discussion
Problem 26:
You are pushing your desk across the floor in a straight line at a steady speed. Which of the following statements about the forces acting on the desk is correct?
Answer: (D) The amount of force that you're exerting on the desk must be equal to the amount of force that friction is exerting on it. [89.6% picked]
Why: Video Discussion
Problem 27:
You have two baseball bats: one a conventional wooden bat and the other a high-tech aluminum bat. The two bats have the same shape and mass, but the aluminum bat has a softer and bouncier surface. When the two bats are swung equally fast at the same pitched ball, the aluminum bat hits the ball farther than the wooden bat because the aluminum bat
Answer: (B) receives a larger fraction of the collision energy and returns almost all of that energy as rebound energy. [82.3% picked]
Why: Video Discussion
Problem 28:
You are riding a carousel at the fair. Suddenly, your horse breaks free from the carousel. Neglecting gravity, in which direction do you travel?
Answer: (C) You continue straight ahead, in the direction of your velocity before the horse broke free. [61.9% picked]
Why: Video Discussion
Problem 29:
Two toy cars roll off a level table side-by-side at the same time and in the same direction The cars soon hit the level floor below the table. The red car weighs twice as much as the blue car, but the blue car left the table at twice the horizontal speed of the red car. In this situation,
Answer: (D) the two cars hit the floor at approximately the same time, but the blue car hits considerably farther from the table than the red car. [91.3% picked]
Why: Video Discussion
Problem 30:
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: (C) the child who jumps forward reaches the water before the child who jumps upward. [81.4% picked]
Why: Video Discussion