ASU Physics 121 Final Exam
A certain planet has an escape speed V. If another planet of the same size has twice the mass as the first planet, its escape speed will be
(√2)V .
A 30.0-kg child sits on one end of a long uniform beam having a mass of 20.0 kg, and a 40.0-kg child sits on the other end. The beam balances when a fulcrum is placed below the beam a distance 1.10 m from the 30.0-kg child. How long is the beam?
1.98 m
If the mass of the earth and all objects on it were suddenly doubled, but the size remained the same, the acceleration due to gravity at the surface would become
2 times what it now is.
A uniform solid sphere has a moment of inertia I about an axis tangent to its surface. What is the moment of inertia of this sphere about an axis through its center?
2/7 I
A satellite in a circular orbit of radius R around planet X has an orbital period T. If Planet X had one-fourth as much mass, the orbital period of this satellite in an orbit of the same radius would be
2T.
A nonuniform, 80.0-g, meterstick balances when the support is placed at the 51.0-cm mark. At what location on the meterstick should a 5.00-g tack be placed so that the stick will balance at the 50.0 cm mark?
34.0 cm
Planet Z-34 has a mass equal to 1/3 that of Earth, a radius equal to 1/3 that of Earth, and an axial spin rate 1/2 that of Earth. With g representing, as usual, the acceleration due to gravity on the surface of Earth, the acceleration due to gravity on the surface of Z-34 is
3g.
A figure skater rotating at 5.00 rad/s with arms extended has a moment of inertia of 2.25 kg·m2. If the arms are pulled in so the moment of inertia decreases to 1.80 kg·m2, what is the final angular speed?
6.25 rad/s
Shown below are the velocity and acceleration vectors for a person in several different types of motion. In which case is the person slowing down and turning to his right?
Acceleration is diagonally up and to the left, velocity is straight down.
Alice and Tom dive from an overhang into the lake below. Tom simply drops straight down from the edge, but Alice takes a running start and jumps with an initial horizontal velocity of 25 m/s. Neither person experiences any significant air resistance. Compare the time it takes each of them to reach the lake below.
Alice and Tom will reach the surface of the lake at the same time.
Two stones, one of mass m and the other of mass 2m, are thrown directly upward with the same velocity at the same time from ground level and feel no air resistance. Which statement about these stones is true?
At its highest point, the heavier stone will have twice as much gravitational potential energy as the lighter one because it is twice as heavy.
Two identical balls are thrown directly upward, ball A at speed v and ball B at speed 2v, and they feel no air resistance. Which statement about these balls is correct?
Ball B will go four times as high as ball A because it had four times the initial kinetic energy.
Block 1 and block 2 have the same mass, m, and are released from the top of two inclined planes of the same height making 30° and 60° angles with the horizontal direction, respectively. If the coefficient of friction is the same in both cases, which of the blocks is going faster when it reaches the bottom of its respective incline?
Block 2 is faster.
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.
A girl and a boy are riding on a merry-go-round that is turning at a constant rate. The girl is near the outer edge, and the boy is closer to the center. Who has greater tangential acceleration?
Both the girl and the boy have zero tangential acceleration.
Earth's orbit around the Sun is slightly elliptical. Thus, Earth actually gets closer to the Sun during part of the year. What happens to Earth's orbital speed when it is closer to the Sun?
Earth's orbital speed is greater when it is closer to the Sun than when it is farther from the Sun.
A restoring force of magnitude F acts on a system with a displacement of magnitude x. In which of the following cases will the system undergo simple harmonic motion?
F ∝ x
A frictionless pendulum released from 65 degrees with the vertical will vibrate with the same frequency as if it were released from 5 degrees with the vertical because the period is independent of the amplitude and mass.
False
In order to get an object moving, you must push harder on it than it pushes back on you.
False.
A dumbbell-shaped object is composed by two equal masses, m, connected by a rod of negligible mass and length r. If I1 is the moment of inertia of this object with respect to an axis passing through the center of the rod and perpendicular to it and I2 is the moment of inertia with respect to an axis passing through one of the masses, it follows that
I2 > I1.
A slender uniform rod 100.00 cm long is used as a meter stick. Two parallel axes that are perpendicular to the rod are considered. The first axis passes through the 50-cm mark and the second axis passes through the 30-cm mark. What is the ratio of the moment of inertia through the second axis to the moment of inertia through the first axis?
I2/I1 = 1.5
Suppose that a car traveling to the west (the -x direction) begins to slow down as it approaches a traffic light. Which statement concerning its acceleration in the x direction is correct?
Its acceleration is positive but its velocity is negative.
Consider a uniform solid sphere of radius R and mass M rolling without slipping. Which form of its kinetic energy is larger, translational or rotational?
Its translational kinetic energy is larger than its rotational kinetic energy.
You are standing in a moving bus, facing forward, and you suddenly fall forward as the bus comes to an immediate stop. The force that pushes forward on you as the bus stops is
No forward force is acting on you as the bus stops.
A heavy boy and a lightweight girl are balanced on a massless seesaw. If they both move forward so that they are one-half their original distance from the pivot point, what will happen to the seesaw? Assume that both people are small enough compared to the length of the seesaw to be thought of as point masses.
Nothing will happen; the seesaw will still be balanced.
Two weights are connected by a massless wire and pulled upward with a constant speed of 1.50 m/s by a vertical pull P. The tension in the wire is T (see figure). Which one of the following relationships between T and P must be true?
P = T + 25 N
Two planets having equal masses are in circular orbit around a star. Planet A has a smaller orbital radius than planet B. Which statement is true?
Planet A has more kinetic energy, less potential energy, and less mechanical energy (potential plus kinetic) than planet B.
Consider two less-than-desirable options. In the first you are driving 30 mph and crash head-on into an identical car also going 30 mph. In the second option you are driving 30 mph and crash head-on into a stationary brick wall. In neither case does your car bounce off the thing it hits, and the collision time is the same in both cases. Which of these two situations would result in the greatest impact force?
The force would be the same in both cases.
A girl and a boy are riding on a merry-go-round that is turning at a constant rate. The girl is near the outer edge, and the boy is closer to the center. Who has greater linear speed?
The girl has greater linear speed.
A frictionless pendulum clock on the surface of the earth has a period of 1.00 s. On a distant planet, the length of the pendulum must be shortened slightly to have a period of 1.00 s. What is true about the acceleration due to gravity on the distant planet?
The gravitational acceleration on the planet is slightly less than g.
Two objects attract each other gravitationally. If the distance between their centers decreases by a factor of 2, how does the gravitational force between them change?
The gravitational force increases by a factor of 4.
A baseball is located at the surface of the earth. Which statements about it are correct? (There may be more than one correct choice.)
The gravitational force on the ball due to the earth is exactly the same as the gravitational force on the earth due to the ball.
In a lab environment, you are investigating the impulse of a force exerted on a brick when the brick's speed is reduced from 2.5 m/s to a complete stop. First, you allow the brick to slam into a secured piece of wood, bringing the brick to a sudden stop. Second, you allow the brick to plow into a large slab of gelatin so that the brick comes to a gradual halt. In which situation is there a greater impulse of the force on the brick?
The impulse is the same in both situations.
A horizontal disk rotates about a vertical axis through its center. Point P is midway between the center and the rim of the disk, and point Q is on the rim. If the disk turns with constant angular velocity, which of the following statements about it are true? (There may be more than one correct choice.)
The linear acceleration of Q is twice as great as the linear acceleration of P. Q is moving twice as fast as P.
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.
When a constant force acts on an object, what does the object's change in momentum depend upon?
The magnitude of the force. The mass of the object. The change in the velocity of the object. The time interval during which the force acts.
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.
Two planets, planet A and planet B, have the same surface gravity. However, planet B has twice the radius of planet A. How does the mass of planet B compare to the mass of planet A?
The mass of planet B is four times the mass of planet A.
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.
A constant net torque is applied to a rotating object. Which of the following best describes the object's motion?
The object will rotate with constant angular acceleration.
A heavy boy and a lightweight girl are balanced on a massless seesaw. The boy moves backward, increasing his distance from the pivot point. What happens to the seesaw?
The side the boy is sitting on will tilt downward.
A solid sphere, solid cylinder, and a hollow pipe all have equal masses and radii and are of uniform density. If the three are released simultaneously at the top of an inclined plane and roll without slipping, which one will reach the bottom first?
The solid sphere.
A girl throws a stone from a bridge. Consider the following ways she might throw the stone. The speed of the stone as it leaves her hand is the same in each case, and air resistance is negligible. Case A: Thrown straight up. Case B: Thrown straight down. Case C: Thrown out at an angle of 45° above horizontal. Case D: Thrown straight out horizontally. In which case will the speed of the stone be greatest when it hits the water below?
The speed will be the same in all cases.
Two objects have masses m and 5m, respectively. They both are placed side by side on a frictionless inclined plane and allowed to slide down from rest.
The two objects reach the bottom of the incline at the same time.
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.
A red ball with a velocity of +3.0 m/s collides head-on with a yellow ball of equal mass moving with a velocity of −2.0 m/s. What is the velocity of the two balls after the elastic collision?
The velocity of the red ball is −2.0 m/s; the velocity of the yellow ball is +3.0 m/s.
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.
Why does a satellite in a circular orbit travel at a constant speed?
There is no component of force acting along the direction of motion of the satellite.
Two objects are thrown from the top of a tall building and experience no appreciable air resistance. One is thrown up, and the other is thrown down, both with the same initial speed. What are their speeds when they hit the street?
They are traveling at the same speed.
A satellite is orbiting the earth. If a payload of material is added until it doubles the satellite's mass, the earth's pull of gravity on this satellite will double but the satellite's orbit will not be affected.
True
If a force always acts perpendicular to an object's direction of motion, that force cannot change the object's kinetic energy.
True.
Consider what happens when you jump up in the air. Which of the following is the most accurate statement?
When you push down on the earth with a force greater than your weight, the earth will push back with the same magnitude force and thus propel you into the air.
A 615 N student standing on a scale in an elevator notices that the scale reads 645 N. From this information, the student knows that the elevator must be moving
You cannot tell if it is moving upward or downward.
When a rigid body rotates about a fixed axis, all the points in the body have the same
angular acceleration.
You swing a bat and hit a heavy box with a force of 1500 N. The force the box exerts on the bat is
exactly 1500 N whether or not the box moves.
Because the earth's orbit is slightly elliptical, the earth actually gets closer to the sun during part of the year. When the earth is closer to the sun its orbital speed is
greater than when the earth is farthest away from the sun.
If we double only the amplitude of a vibrating ideal mass-and-spring system, the mechanical energy of the system
increases by a factor of 4.
An object is moving to the right, and experiencing a net force that is directed to the right. The magnitude of the force is decreasing with time. The speed of the object is
increasing.
For general projectile motion, when the projectile is at the highest point of its trajectory
its velocity is perpendicular to the acceleration.
A box of mass m is pressed against (but is not attached to) an ideal spring of force constant k and negligible mass, compressing the spring a distance x. After it is released, the box slides up a frictionless incline as shown in the figure and eventually stops. If we repeat this experiment but instead compress the spring a distance of 2x
just as it moves free of the spring, the box will be traveling twice as fast as before.
If an object travels at a constant speed in a circular path, the acceleration of the object is
larger in magnitude the smaller the radius of the circle.
Two bodies P and Q on a smooth horizontal surface are connected by a light cord. The mass of P is greater than that of Q. A horizontal forceF⃗ (of magnitude F) is applied to Q as shown in the figure, accelerating the bodies to the right. The magnitude of the force exerted by the connecting cord on body P will be
less than F but not zero.
A ball drops some distance and gains 30 J of kinetic energy. Do NOT ignore air resistance. How much gravitational potential energy did the ball lose?
more than 30 J
A small glider is coasting horizontally when suddenly a very heavy piece of cargo falls out of the bottom of the plane. You can neglect air resistance. Just after the cargo has fallen out
neither the cargo nor the plane change speed.
Suppose you are playing hockey on a new-age ice surface for which there is no friction between the ice and the hockey puck. You wind up and hit the puck as hard as you can. After the puck loses contact with your stick, the puck will
not slow down or speed up.
In the figure, determine the character of the collision. The masses of the blocks, and the velocities before and after are given. The collision is Figure Before shows two blocks on a horizontal surface. The right block has mass of 6 kilograms and velocity of 0.2 meters per second directed to the left. The left block has mass of 4 kilograms and velocity of 1.8 meters per second directed to the right. Figure After shows the same two blocks on a horizontal surface. The right block has velocity of 1.4 meters per second directed to the right. The left block has velocity of 0.6 meters per second directed to the left.
perfectly elastic.
A uniform disk, a uniform hoop, and a uniform solid sphere are released at the same time at the top of an inclined ramp. They all roll without slipping. In what order do they reach the bottom of the ramp?
sphere, disk, hoop
The reason an astronaut in an earth satellite feels weightless is that
the astronaut is falling.
Two objects, one of mass m and the other of mass 2m, are dropped from the top of a building. When they hit the ground
the heavier one will have twice the kinetic energy of the lighter one.
While an object is in projectile motion (with upward being positive) with no air resistance
the horizontal component of its velocity remains constant and the vertical component of its acceleration is equal to -g.
A 1.0-kg block and a 2.0-kg block are pressed together on a horizontal frictionless surface with a compressed very light spring between them. They are not attached to the spring. After they are released and have both moved free of the spring
the lighter block will have more kinetic energy than the heavier block.
A box of mass m is pressed against (but is not attached to) an ideal spring of force constant k and negligible mass, compressing the spring a distance x. After it is released, the box slides up a frictionless incline as shown in the figure and eventually stops. If we repeat this experiment with a box of mass 2m
the lighter box will go twice as high up the incline as the heavier box.
In simple harmonic motion, the speed is greatest at that point in the cycle when
the magnitude of the acceleration is a minimum.
In an INELASTIC collision between two objects
the momentum of the system is conserved but the kinetic energy of the system is not conserved.
If the torque on an object adds up to zero
the object could be both turning and accelerating linearly.
Alice and Tom dive from an overhang into the lake below. Tom simply drops straight down from the edge, but Alice takes a running start and jumps with an initial horizontal velocity of 25 m/s. Neither person experiences any significant air resistance. Just as they reach the lake below
the speed of Alice is larger than that of Tom.
A ball is tossed vertically upward. When it reaches its highest point (before falling back downward)
the velocity is zero, the acceleration is directed downward, and the force of gravity acting on the ball is directed downward.
The angular momentum of a system remains constant
when no torque acts on the system.
The position x of an object varies with time t. For which of the following equations relating x and t is the motion of the object simple harmonic motion? (There may be more than one correct choice.)
x=2cos(3t−1) x=8cos3t x=5sin3t
A stalled car is being pushed up a hill at constant velocity by three people. The net force on the car is
zero.
A mass M is attached to an ideal massless spring. When this system is set in motion with amplitude A, it has a period T. What is the period if the amplitude of the motion is increased to 2A?
T
Two objects having masses m1 and m2 are connected to each other as shown in the figure and are released from rest. There is no friction on the table surface or in the pulley. The masses of the pulley and the string connecting the objects are completely negligible. What must be true about the tension T in the string just after the objects are released?
T < m2 g
A box of mass m is pulled with a constant acceleration a along a horizontal frictionless floor by a wire that makes an angle of 15° above the horizontal. If T is the tension in this wire, then
T > ma.
A satellite of mass m has an orbital period T when it is in a circular orbit of radius R around the earth. If the satellite instead had mass 4m, its orbital period would be
T.
Point P in the figure indicates the position of an object traveling at constant speed clockwise around the circle. Which arrow best represents the direction of the acceleration of the object at point P?
The acceleration points towards the center of the circle.
A girl moves quickly to the center of a spinning merry-go-round, traveling along the radius of the merry-go-round. Which of the following statements are true?
The angular speed of the system increases. The moment of inertia of the system decreases.
Starting from rest, a solid sphere rolls without slipping down an incline plane. At the bottom of the incline, what does the angular velocity of the sphere depend upon?
The angular velocity depends upon the height of the incline. The angular velocity depends upon the radius of the sphere.
A lump of putty and a rubber ball have equal mass. Both are thrown with equal speed against a wall. The putty sticks to the wall. The ball bounces back at nearly the same speed with which it hit the wall. Which object experiences the greater momentum change?
The ball experiences the greater momentum change.
Two equal forces are applied perpendicular to a door. The first force is applied at the midpoint of the door; the second force is applied at the doorknob. Which force exerts the greater torque?
The force applied at the doorknob exerts the greater torque.
A potential energy function for system 1 is given by U1(x)=Cx2+Bx3. The potential energy function for system 2 is given by U2(x)=A+Cx2+Bx3, where A is a positive quantity. How does the force on system 1 relate to the force on system 2 at a given position?
The force is identical on the two systems.
A pilot drops a package from a plane flying horizontally at a constant speed. Neglecting air resistance, when the package hits the ground the horizontal location of the plane will
be over the package.
In a perfectly ELASTIC collision between two perfectly rigid objects
both the momentum and the kinetic energy of the system are conserved.
