UW Physics 114 Mastering Questions
A police car travels at 37.8 m/s due east while in pursuit of a vehicle that is traveling at 33.4 m/s due east. What is the velocity of the vehicle relative to the police car?
-4.4 m/s (x^)
Suppose a runner completes one lap around a 400-m track in a time of 50 s. Calculate the magnitude of the average velocity of the runner.
0 m/s (his displacement is zero if his starting point = his ending point)
On Mars, where air resistance is negligible, an astronaut drops a rock from a cliff and notes that the rock falls about d meters during the first t seconds of its fall. Assuming the rock does not hit the ground first, how far will it fall during the first 4t seconds of its fall?
16d
Consider the video tutorial you just watched. Suppose that we duplicate this experimental setup in an elevator. What will the spring scale read if the elevator is moving upward at constant speed?
18 N (Since the elevator is not accelerating, the reading on the scale is the same as in the video.)
The sum of the x components of vectors A and B in (Figure 1) is ___.
4
What is the velocity of the police car relative to the vehicle?
4.4 m/s (x^)
On the Moon, where air resistance is negligible, an astronaut drops a rock from a cliff and notes that the rock has a speed v after falling from its point of release for a time t. Assuming that the rock does not hit the ground first, how fast will it be moving after it has fallen for a time 4t from its point of release?
4v
Consulting the graph shown in (Figure 1) , determine the object's average velocity over the time interval from 2 to 4 seconds.
5 m/s
Starting from your campsite you walk 3.0 km east, 6.0 km north, 1.0 km east, and then 4.0 km west. How far are you from your campsite?
6.0 km
Vector A⃗ has a magnitude of 2.00 m and vector B⃗ has a magnitude of 5.00 m. If the direction of each vector is unknown, what is the largest possible value for the magnitude of A⃗ −B⃗ ?
7.00 m
Suppose a runner completes one lap around a 400-m track in a time of 50 s. Calculate the average speed of the runner.
8 m/s
A car drives with constant speed on an elliptical track, as shown in the figure (Figure 1) .Rank the points A, B, and C in order of decreasing likelihood that the car might skid. Rank the points from most likely to least likely for car to skid. To rank items as equivalent, overlap them.
A, B, C
When launched, the human cannonball's initial velocity has a positive x-component and a positive y-component. Rank the vertical velocity components at points A through E from most positive to most negative.
A, B, C, D, E
A football player kicks a football in a field goal attempt. When the football reaches its maximum height, what is the relationship between the direction of the velocity and acceleration vectors? Assume air resistance is negligible.
At the maximum height, the velocity and acceleration vectors are perpendicular to each other.
Which of the following best describes how to calculate the average acceleration of any object?
Average acceleration is always equal to the change in velocity of an object divided by the time interval.
Which of the following equations correctly expresses the relation between vectors A⃗ , B⃗ , and C⃗ shown in the figure? (problem 2)
A⃗ +B⃗ +C⃗ =0
A puck attached to a string undergoes circular motion on an air table. If the string breaks at the point indicated in the figure (Figure 1) , is the subsequent motion of the puck best described by path A, B, C, or D?
B
Use the motion diagram in (Figure 1) showing the trajectory of a human cannonball to answer Parts A through D. No air resistance acts on the human cannonball. How does the vertical acceleration at point A compare to the vertical acceleration at point C?
Both accelerations are equal to free fall acceleration.
In the situation shown in the figure, a person is pulling with a constant, nonzero force F⃗ on string 1, which is attached to block A. Block A is also attached to block B via string 2, as shown. For this problem, assume that neither string stretches and that friction is negligible. Both blocks have finite (nonzero) mass. Which one of the following statements correctly descibes the relationship between the accelerations of blocks A and B?
Both blocks will have the same acceleration
Which of the following equations correctly expresses the relation between vectors A⃗ , B⃗ , and C⃗ shown in the figure? (problem 1)
B⃗ =A⃗ +C⃗
Which of the motion diagrams in the figure below best matches the motion of the bungee jumper shown in the video?
C (Because the video only follows the free fall portion of the jump, the correct motion diagram shows constant downward acceleration.)
Vector A⃗ has a magnitude of 3.00 and is directed parallel to the negative y-axis and vector B⃗ has a magnitude of 3.00 and is directed parallel to the positive y-axis. Determine the magnitude and direction angle (as measured counterclockwise from the positive x-axis) of vector C⃗ , if C⃗ =A⃗ −B⃗ .
C = 6.00; θ = 270˚
Four cars undergo acceleration as described by the data in the following table.
Car B, Car A, Car D, Car C (Correct The average accelerations, from most positive to most negative, are as follows: (B) 4 m/s2, (A) 3 m/s2, (D) 2.5 m/s2, and (C) −3 m/s2.)
Three cars drive around a perfectly circular track. The speedometers in the figure below show the speed of each car over the same 10-s time interval. Which of the cars are accelerating?
Cars A, B, and C (All three cars are accelerating because the directions of their velocity vectors change constantly as they drive in a circle. In addition, the speeds of cars A and B are changing, which also indicates acceleration.)
A force pair is produced when a tennis racket strikes a tennis ball. Which of the following best explains why the tennis ball does not have zero net force acting on it?
Each half of the force pair acts on a different object.
The first physicist gets a second physicist to help. They both push on the crate, parallel to the surface of the incline, and it moves at constant speed up the incline. How does the force exerted by the two physicists on the crate compare with the force of friction on the crate?
F(two physicists) is greater than F(friction)
During which interval is the largest amount of energy required to stretch the spring?
From x = 2d to x = 3d
To hang a pot of flowers, a gardener uses two wires - one attached horizontally to a wall, the other sloping upward at an angle θ of and attached to the ceiling.(Figure 1) Which of the three graphs (A, B, or C) in the figure shows an accurate plot of the tensions T1 and T2 as a function of the angle θ? (Figure 2)
Graph B
According to Newton's first law, when the net force acting on an object is zero, the object must _____
Have constant velocity.
How does the magnitude of the horizontal velocity change as the human cannonball passes through points A, B, C, D, and E?
It does not change.
Choose the best explanation from among the following:
Locked-up breaks lead to sliding (kinetic) friction, which is less than rolling (static) friction.
Consider the video demonstration that you just watched. Which of the following changes would make it more likely for the ball to hit both the white can and the green can?
None of the above
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.
Which of the following statements is/are true?
Power can be considered the rate at which energy is transformed. A person's power output limits the amount of work that he or she can do in a given time span. Power can be considered the rate at which work is done. The SI unit of power is the watt.
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?
Spring A requires the same amount of energy as spring B
How does the magnitude of the tension in string 1, T1, compare with the tension in string 2, T2?
T1 > T2
Choose the best explanation from among the following:
T2 is greater than T1 at all angles, and is equal to mg at θ = 90°
The same net force is applied to two different objects. The second object has twice the mass of the first object. Compare the acceleration of the two objects.
The acceleration of object 1 is twice the acceleration of object 2
The figure shows the velocity versus time graph for a car driving on a straight road. Which of the following best describes the acceleration of the car?
The acceleration of the car is positive and decreasing.
At what angle, above the horizon, should a cannon be fired in order for the cannon ball to obtain the greatest horizontal range? Assume air resistance is negligible.
The cannon should be fired at an angle of 45° above the horizon.
In general, how does the coefficient of static friction compare to the coefficient of kinetic friction for the same two materials?
The coefficient of static friction is greater than the coefficient of kinetic friction.
A large truck collides head-on with a small car. The car is severely damaged as a result of the collision. According to Newton's third law, how do the forces acting between the truck and car compare during the collision?
The force on the truck is equal to the force on the car.
A physicist attempts to push the crate up the incline. The physicist senses that if he applies slightly more force the crate will move up the incline but cannot muster enough strength to get the motion started. What can you say now about the force of friction acting on the crate?
The frictional force points down the incline
A large crate filled with physics laboratory equipment must be moved up an incline onto a truck. (Figure 1). The crate is at rest on the incline. What can you say about the force of friction acting on the crate?
The frictional force points up the incline
Choose the best explanation from among the following:
The gravitational potential energy depends only on the mass of the ball drop height.
For general projectile motion, which of the following best describes the horizontal component of a projectile's acceleration? Assume air resistance is negligible.
The horizontal component of a projectile's acceleration is zero.
A packing crate is sitting at rest on an inclined loading ramp. How does the magnitude of the force of static friction compare to the other forces acting on the crate?
The magnitude of the force of static friction is equal to the magnitude of the component of the weight of the crate parallel to the inclined ramp
An object is hanging by a string from the ceiling of an elevator. The elevator is moving upward with a constant speed. What is the magnitude of the tension in the string?
The magnitude of the tension in the string is equal to the magnitude of the weight of the object.
An object is hanging by a string from the ceiling of an elevator. The elevator is slowing down while moving upward. What is the magnitude of the tension in the string?
The magnitude of the tension in the string is less than the magnitude of the weight of the object
Suppose you are hiking along a trail. Make a comparison between the magnitude of your displacement and your distance traveled.
The magnitude of your displacement can be equal to your distance traveled. The magnitude of your displacement can be less than your distance traveled
Choose the best explanation from among the following:
The net force acting on the blocks is the same, but the total mass that must be accelerated is greater.
An object is moving with constant velocity. Which of the following best describes the force(s) acting on the object?
The net force acting on the object is zero.
An object moves in a circular path at a constant speed. What is the direction of the net force acting on the object?
The net force is directed toward the center of the circular path
A person applies a 50 N force on a crate, causing it to move horizontally at a constant speed through a distance of 10 m. What is the net work done on the crate
The net work done on the crate is zero joules
Choose the best explanation from among the following:
The normal force is the same in the two cases, and friction is independent of surface area.
If the net work done on an object is positive, what can you conclude about the object's motion? Assume the object is in the absence of any other forces or friction.
The object is speeding up
Suppose that you toss a rock upward so that it rises and then falls back to the earth. If the acceleration due to gravity is 9.8 m/sec2, what is the rock's acceleration at the instant that it reaches the top of its trajectory (where its velocity is momentarily zero)? Assume that air resistance is negligible.
The rock has a downward acceleration of 9.8m/s^2
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
Two identical cars are driving in opposite directions at the same speed. Their kinetic energies have ____.
The same magnitude and sign
A swimmer is determined to cross a river that flows due south with a strong current. Initially, the swimmer is on the west bank desiring to reach a camp directly across the river on the opposite bank. In which direction should the swimmer head?
The swimmer should swim northeast.
On a straight road, a car speeds up at a constant rate from rest to 20 m/s over a 5 second interval and a truck slows at a constant rate from 20 m/s to a complete stop over a 10 second interval. How does the distance traveled by the truck compare to that of the car?
The truck travels twice as far as the car.
Two objects are moving at equal speed along a level, frictionless surface. The second object has twice the mass of the first object. They both slide up the same frictionless incline plane. Which object rises to a greater height?
The two objects rise to the same height
An object moves in a circular path at a constant speed. What is the relationship between the directions of the object's velocity and acceleration vectors?
The velocity and acceleration vectors are perpendicular
For general projectile motion, which of the following best describes the vertical component of a projectile's acceleration? Assume air resistance is negligible.
The vertical component of a projectile's acceleration remains a nonzero constant
Atwood's machine consists of two masses connected by a string that passes over a pulley, as shown in the figure.(Figure 1) The acceleration of the masses for general m1 and m2 is a=(m2−m1m2+m1)g. In the specific case m1 = 3.1kg and m2 = 4.4kg acceleration of the blocks a=1.7m/s2. Suppose m1 and m2 are both increased by 1 kg. Does the acceleration of the blocks increase, decrease, or stay the same?
decrease
The work-energy theorem states that a force acting on a particle as it moves over a ______ changes the ______ energy of the particle if the force has a component parallel to the motion.
distance/kinetic
Recall the portion of the video in which the girl pushes her brother on the sled at constant velocity. The pushing force she exerts on the sled is _____ the frictional force the ground exerts on the sled.
equal to
You push two identical bricks across a tabletop with constant speed, v, as shown in the figure. In case 1, you place the bricks end to end; in case 2, you stack the bricks one on top of the other.(Figure 1) Is the force of kinetic friction in case 1 greater than, less than, or equal to the force of kinetic friction in case 2?
equal to
Ball 1 is thrown to the ground with an initial downward speed; ball 2 is dropped to the ground from rest. Assuming the balls have the same mass and are released from the same height, is the change in gravitational potential energy of ball 1 greater than, less than, or equal to the change in gravitational potential energy of ball 2?
equal to the change in gravitational potential energy of ball 2
The video identifies the force pair produced when an apple falls through the air. Which force belongs in a free-body diagram of the apple?
force of Earth on apple
To illustrate the work-energy concept, consider the case of a stone falling from xi to xf under the influence of gravity. Using the work-energy concept, we say that work is done by the gravitational _____, resulting in an increase of the ______ energy of the stone.
force/kinetic
Two drivers traveling side-by-side at the same speed suddenly see a deer in the road ahead of them and begin braking. Driver 1 stops by locking up his brakes and screeching to a halt; driver 2 stops by applying her brakes just to the verge of locking, so that the wheels continue to turn until her car comes to a complete stop. All other factors being equal, is the stopping distance of driver 1 greater than, less than, or equal to the stopping distance of driver 2?
greater than
You are pulling your little sister on her sled across an icy (frictionless) surface. When you exert a constant horizontal force of 110 N , the sled has an acceleration of 2.4 m/s2 . If the sled has a mass of 9.0 kg , what is the mass of your little sister?
m = 37 kg
The amount of kinetic energy an object has depends on its mass and its speed. Rank the following sets of oranges and cantaloupes from least kinetic energy to greatest kinetic energy. If two sets have the same amount of kinetic energy, place one on top of the other.
mass 4m speed 1/4v, total mass 2m speed 1/2v, mass m speed v, total mass 4m speed v = mass 4m speed v
A motorcycle drives up a steeply inclined ramp. The work done on the motorcycle by the Earth's gravitational force is ____.
negative
The sum of two vectors is the largest when the two vectors are _____.
pointing in the same direction
To calculate the change in kinetic energy, you must know the force as a function of _______. The work done by the force causes the kinetic energy change.
position
This process happens in such a way that total mechanical energy, equal to the ______ of the kinetic and potential energies, is _______.
sum/conserved
An object is at rest on a tabletop. Earth pulls downward on this object with a force equal in magnitude to mg. If this force serves as the action force, what is the reaction force in the action-reaction pair?
the object pulling upward on Earth
During a certain time interval, the net work done on an object is zero joules. We can be certain that ____.
the object's final speed was the same as its initial speed
What explains the dramatically different magnitudes of accelerations that result when a mosquito collides head on with a moving truck?
unequal masses of the bus and the mosquito
A Human Centrifuge To test the effects of high acceleration on the human body, the National Aeronautics and Space Administration (NASA) has constructed a large centrifuge at the Manned Spacecraft Center in Houston. In this device, astronauts are placed in a capsule that moves in a circular path with a radius of 15 m. If the astronauts in this centrifuge experience a centripetal acceleration 9.0 times that of gravity, what is the linear speed of the capsule?
v = 36 m/s
As an airplane taxies on the runway with a speed of 17.0 m/s , a flight attendant walks toward the tail of the plane with a speed of 1.22 m/s. What is the flight attendant's speed relative to the ground?
v(rel) = 15.8 m/s
Suppose a rocket launches with an acceleration of 32.0 m/s2 . What is the apparent weight of an 95-kg astronaut aboard this rocket
w(a) = 4000 N
An ant walks slowly away from the top of a bowling ball, as shown in the figure.If the ant starts to slip when the normal force on its feet drops below one-half its weight, at what angle θ does slipping begin?
θ = 60°
Which of the following best describes the acceleration of a bungee jumper during free fall?
constant (Free fall acceleration is constant and has a value of 9.8 m/s^2)
Which of the following statements is/are true?
The work done by a nonconservative force depends on the the path taken. A potential energy function can be specified for a conservative force. A conservative force permits a two-way conversion between kinetic and potential energies
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
An object weighing 20 N moves horizontally toward the right a distance of 5.0 m. What is the work done on the object by the force of gravity?
The work done on the object by the force of gravity is zero joules.
Rather than ascribing the increased kinetic energy of the stone to the work of gravity, we now (when using potential energy rather than work-energy) say that the increased kinetic energy comes from the ______ of the _______ energy.
change/potential
The work done by a conservative force is indicated in the figure for a variety of different paths connecting the points A and B. What is the work done by this force on path 1?
W1 = -3 J
What is the work done by this force on path 2?
W2 = -4 J
Suppose that C⃗ =A⃗ −B⃗ . Under what circumstances is the length of C⃗ has to equal to the sum of the lengths of A⃗ has and B⃗ has?
When A⃗ and B⃗ point in opposite directions
Imagine holding a basketball in both hands, throwing it straight up as high as you can, and then catching it when it falls. At which points in time does a zero net force act on the ball? Ignore air resistance.
When you hold the ball still in your hands after catching it When you hold the ball still in your hands before it is thrown
A ball is thrown straight upward. How does the sign of the work done by gravity while the ball is traveling upward compare with the sign of the work done by gravity while the ball is traveling downward?
Work done by gravity is negative while the ball is traveling upward and positive while the ball is traveling downward.
Is the vertical component of velocity ever zero? If so, where?
Yes, it is zero at point C
Which of the following is a vector quantity?
acceleration velocity momentum force displacement
An elevator moves straight upward at a constant speed. Newton's first law predicts that the net force acting on the elevator will _____.
be zero.
