Physics Unit 4
A 35-N bucket of water is lifted vertically 3.0 m and then returned to its original position. How much work did gravity do on the bucket during this process?
0 J
A heavy dart and a light dart are launched horizontally on a frictionless table by identical ideal springs. Both springs were initially compressed by the same amount. Which of the following statements about these darts are correct? (There could be more than one correct choice.)
-Both darts had the same initial elastic potential energy. - The lighter dart leaves the spring moving faster than the heavy dart. - The darts both have the same kinetic energy just as they move free of the spring.
For an INELASTIC collision, which of the following statements are true?
-Kinetic energy is gained. -Kinetic energy is lost. -Momentum is conserved.
A 5-kg ball collides inelastically head-on with a 10-kg ball, which is initially stationary. Which of the following statements is true?
-The magnitude of the change of velocity the 5-kg ball experiences is greater than that of the 10-kg ball. -The magnitude of the change of the momentum of the 5-kg ball is equal to the magnitude of the change of momentum of the 10-kg ball.
Which of the following actions, if done independently, would increase the maximum height reached by the ball?
-increasing the spring constant k - increasing the distance the spring is compressed - decreasing the mass of the ball
A force produces power P by doing work W in a time T. What power will be produced by a force that does six times as much work in half as much time?
12P
When you drop a pebble from height H, it reaches the ground with kinetic energy K if there is no air resistance. From what height should you drop it so it will reach the ground with twice as much kinetic energy?
2H
When you throw a pebble straight up with initial speed V, it reaches a maximum height H with no air resistance. At what speed should you throw it up vertically so it will go twice as high?
2√ V
A tiger is running in a straight line. If we double both the mass and speed of the tiger, the magnitude of its momentum will increase by what factor?
4
When you drop a pebble from height H, it reaches the ground with speed V if there is no air resistance. From what height should you drop it so it will reach the ground with twice speed?
4H
A spring-loaded dart gun is used to shoot a dart straight up into the air, and the dart reaches a maximum height of 24 meters. The same dart is shot up a second time from the same gun, but this time the spring is compressed only half as far (compared to the first shot). How far up does the dart go this time (neglect all friction and assume the spring is ideal)?
6.0 m
A 4.0 kg object is moving with speed 2.0 m/s. A 1.0 kg object is moving with speed 4.0 m/s. Both objects encounter the same constant braking force, and are brought to rest. Which object travels the greater distance before stopping?
Both objects travel the same distance.
You and your friend, who weighs the same as you, want to go to the top of the Eiffel Tower. Your friend takes the elevator straight up. You decide to walk up the spiral stairway, taking longer to do so. Compare the gravitational potential energy of you and your friend, after you both reach the top.
Both of you have the same amount of gravitational potential energy at the top.
Two objects of different mass have equal, non-zero kinetic energies. Which object has the greater magnitude momentum?
the heavier object
Two blocks of ice, one four times as heavy as the other, are at rest on a frozen lake. A person pushes each block the same distance d. Ignore friction and assume that an equal force F⃗ is exerted on each block. Which of the following statements is true about the kinetic energy of the heavier block after the push?
It is equal to the kinetic energy of the lighter block.
A truck has four times the mass of a car and is moving with twice the speed of the car. If K t and K c refer to the kinetic energies of truck and car respectively, it is correct to say that
K t = 16K c.
For an elastic collision, which of the following statements are true?
Momentum is conserved. Kinetic energy is conserved.
A very light ping-pong ball moving east at a speed of 4 m/s collides with a very heavy stationary bowling ball. The Ping-Pong ball bounces back to the west, and the bowling ball moves very slowly to the east. Which object experiences the greater magnitude impulse during the collision?
Neither; both experienced the same magnitude impulse.
Person B does twice the work of person A, and in one-half of the time . How does the power output of person B compare to person A?
Person B has four times the power output of person A.
Now consider two springs A and B that are attached to a wall. Spring A has a spring constant that is four times that of the spring constant of spring B. If the same amount of energy is required to stretch both springs, what can be said about the distance each spring is stretched?
Spring A must stretch half the distance spring B stretches.
Two identical springs are attached to two different masses, MA and MB, where MA is greater than MB. The masses lie on a frictionless surface. Both springs are compressed the same distance, d, as shown in the figure. Which of the following statements descibes the energy required to compress spring A and spring B? (Figure 2)
Spring A requires the same amount of energy as spring B.
A firecracker explodes in midair and breaks up into many fragments. Which of the following statements are true regarding conditions immediately before and immediately after the explosion: I. The total momentum of the fragments is equal to the original momentum of the firecracker. II. The total kinetic energy of the fragments is equal to the original kinetic energy of the firecracker
Statement I only
Which one has larger kinetic energy: a 500-kg object moving at 40 m/s or a 1000-kg object moving at 20 m/s?
The 500-kg object
Two cyclists who weigh the same and have identical bicycles ride up the same mountain, both starting at the same time. Joe rides straight up the mountain, and Bob rides up the longer road that has a lower grade. Joe gets to the top before Bob. Ignoring friction and wind resistance, which one of the following statements is true?
The amount of work done by Joe is equal to the amount of work done by Bob, but the average power exerted by Joe is greater than that of Bob.
Two blocks of ice, one four times as heavy as the other, are at rest on a frozen lake. A person pushes each block the same distance d. Ignore friction and assume that an equal force F⃗ is exerted on each block. Now assume that both blocks have the same speed after being pushed with the same force F⃗ . What can be said about the distances the two blocks are pushed?
The heavy block must be pushed 4 times farther than the light block.
Assume that a pitcher throws a baseball so that it travels in a straight line parallel to the ground. The batter then hits the ball so it goes directly back to the pitcher along the same straight line. Define the direction the pitcher originally throws the ball as the +x direction.
The impulse on the ball caused by the bat will be in the negative x direction.
Two identical balls are thrown vertically upward. The second ball is thrown with an initial speed that is twice that of the first ball. How does the maximum height of the two balls compare?
The maximum height of the second ball is four times that of the first ball.
If the net work done on an object is positive, what can you conclude about the object's motion?
The object is speeding up.
If the net work done on an object is zero, what can you determine about the object's kinetic energy?
The object's kinetic energy remains the same.
A spring is stretched from x=0 to x=d, where x=0 is the equilibrium position of the spring. It is then compressed from x=0 to x=−d. What can be said about the energy required to stretch or compress the spring?
The same amount of energy is required to either stretch or compress the spring.
A stone can slide down one of four different frictionless ramps, as shown in the figure. For which ramp will the speed of the ball be the greatest at the bottom?
The speed of the ball will be the same for all ramps.
A graph depicts force versus position. What represents the work done by the force over the given displacement?
The work done is equal to the area under the curve.
You throw a baseball straight up. Compare the sign of the work done by gravity while the ball goes up with the sign of the work done by gravity while it goes down.
The work is negative on the way up and positive on the way down.
A food Calorie, given on a nutrition label, is actually 1000 calories as defined in chemistry & physics. T or F
True
Batteries contain much less energy than gasoline per unit mass. T or F
True
Energy can be defined as the ability to do work, and it can be turned into heat. T or F
True
Even though energy is conserved, not all forms of energy are useful. T or F
True
Gasoline is used as a fuel since it has a very high energy density (a lot of energy per unit mass). T or F
True
One problem with a Hydrogen car is that the Hydrogen would have to be stored in a pressurized tank in the automobile. T or F
True
People have made solar power cars and drones. T or F
True
Per gram, Uranium stores over a million times more energy than gasoline. T or F
True
Units for energy include the Joule (J), Calorie (Cal), and kilowatt-hour (kWh). T or F
True
If both the graph representing the constant net force and the graph representing the variable net force represent the same impulse acting on the baseball, which geometric properties must the two graphs have in common?
area
Jill does twice as much work as Jack does and in half the time. Jill's power output is
four times Jack's power output.
If the force on an object is in the negative direction, the work it does on the object must be
either positive or negative, depending on the direction the object moves.
In an inelastic collision involving an isolated system, the final total momentum is
exactly the same as the initial momentum.
A stone is held at a height h above the ground. A second stone with four times the mass of the first one is held at the same height. The gravitational potential energy of the second stone compared to that of the first stone is
four times as much.
Which of the following quantities are units of impulse?
kg • m/s and N • s
Is it possible for the kinetic energy of an object to be negative?
no
A pendulum bob swings from point A to point B along the circular arc indicated in the figure. Is the work done on the bob by gravity positive, negative, or zero?
positive
A rubber ball and a lump of clay have equal mass. They are thrown with equal speed against a wall. The ball bounces back with nearly the same speed with which it hit. The clay sticks to the wall. Which one of these objects experiences the greater momentum change?
the ball
Two objects of different masses have momentum of equal, non-zero magnitude. Which object has more kinetic energy?
the lighter object
A pound of chocolate chip cookies has more energy than a pound of TNT. T or F
true
Two blocks of ice, one four times as heavy as the other, are at rest on a frozen lake. A person pushes each block the same distance d. Ignore friction and assume that an equal force F⃗ is exerted on each block. Compared to the speed of the heavier block, what is the speed of the light block after both blocks move the same distance d?
twice as fast
A pendulum bob swings from point A to point B along the circular arc indicated in the figure. Is the work done on the bob by the string positive, negative, or zero?
zero
