PHY 121 Practice Exam 2-4

3.15 How many revolutions per minute (rpm) must a circular, rotating space station (r = 1000 m) rotate to produce an artificial gravity of 9.80 m/s2? A) 0.95 rpm B) 0.83 rpm C) 0.094 rpm D) 0.075 rpm

A) 0.95 rpm

3.4 How many revolutions per minute must a circular, rotating space station of radius 1000 m rotate to produce an artificial gravity of 9.80 m/s2? A) 0.95 rpm B) 0.85 rpm C) 0.65 rpm D) 0.75 rpm

A) 0.95 rpm

3.14 How many rad/s is 25 revolutions per minute equivalent to? A) 2.6 rad/s B) 160 rad/s C) 240 rad/s D) 0.42 rad/s

A) 2.6 rad/s

3.23 A freight car moves along a frictionless level railroad track at constant speed. The car is open on top. A large load of coal is suddenly dumped into the car. What happens to the velocity of the car? A) It decreases. B) It remains the same. C) It increases. D) cannot be determined from the information given

A) It decreases.

3.16 An ice skater performs a pirouette (a fast spin) by pulling in his outstretched arms close to his body. What happens to his moment of inertia about the axis of rotation? A) It does not change. B) It decreases. C) It increases. D) It changes, but it is impossible to tell which way.

A) It does not change. ...but Torri doesn't agree... it decreases

3.2 An object moves in a circular path at a constant speed. Compare the direction of the object's velocity and acceleration vectors. A) The vectors are perpendicular. B) Both vectors point in the same direction. C) The vectors point in opposite directions. D) The question is meaningless, since the acceleration is zero.

A) The vectors are perpendicular.

3.10 In a game of pool, the white cue ball hits the #5 ball and stops, while the #5 ball moves away with the same velocity as the cue ball had originally. The type of collision is A) elastic. B) completely inelastic. C) inelastic. D) any of the above, depending on the mass of the balls.

A) elastic.

2.7 The acceleration of an object is inversely proportional to A) its mass. B) its position. C) the net force acting on it. D) its velocity.

A) its mass.

4.22 The amplitude of a sound wave is A) loudness B) Pitch C) Timber D) none of the above

A) loudness

3.21 Angular displacement is usually express in units of A) radians. B) meters. C) arcs. D) revolutions.

A) radians.

2.20 An object is placed on an inclined plane. The angle of incline is gradually increased until the object begins to slide. The angle at which this occurs is theta. What is the coefficient of static friction between the object and the plane? A) tanθ B) 1/tanθ C) sinθ D) cosθ

A) tanθ

3.13 A rubber ball and a lump of putty 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 putty sticks to the wall. Which objects experiences the greater momentum change? A) the ball B) the putty C) Both experience the same momentum change. D) cannot be determined from the information given

A) the ball

3.20 Two equal forces are applied to a door at the doorknob. The first force is applied perpendicular to the door; the second force is applied at 30° to the plane of the door. Which force exerts the greater torque? A) the first applied perpendicular to the door B) both exert equal non-zero torques C) the second applied at an angle D) both exert zero torques

A) the first applied

4.20 What is the period of a wave with a frequency of 1500 Hz? A) 0.67 μs B) 0.67 ms C) 6.7 s D) 0.67 s

B) 0.67ms

3.19 wo forces are applied to a doorknob, perpendicular to the door. The first force is twice as large as the second force. The ratio of the torque of the first to the torque of the second is A) 1/4. B) 2. C) 1/2. D) 4.

B) 2.

2.13 An object has a mass of 60 kg on the Earth. What is the mass of the object on the surface of the Moon where the acceleration due to gravity is only 1/6 of that on the Earth? A)360kg B) 60kg C) 6.0kg D) 10kg

B) 60kg

4.21 The frequency of a sound wave is A) loudness B) Pitch C) Timber D) none of the

B) Pitch

4.19 A mass is attached to a vertical spring and bobs up and down between points A and B. Where is the mass located when its kinetic energy is a maximum? A) one-fourth of the way between A and B B) at either A or B C) midway between A and B D) none of the above

B) at either A or B

3.7 When an object experiences uniform circular motion, the direction of the net force is A) in the same direction as the motion of the object. B) is directed toward the center of the circular path. C) in the opposite direction of the motion of the object. D) is directed away from the center of the circular path.

B) is directed toward the center of the circular path.

2.3 When the rocket engines on the starship NO-PAIN-NO-GAIN are suddenly turned off, while traveling in empty space, the starship will A) go faster and faster. B) move with constant speed. C) slowly slow down, and then stop. D) stop immediately.

B) move with constant speed.

2.6 A 15-ton truck collides with a 1500-lb car and causes a lot of damage to the car. Since a lot of damage is done on the car A) the force on the truck is greater then the force on the car. B) the force on the truck is equal to the force on the car. C) the truck did not slow down during the collision. D) the force on the truck is smaller than the force on the car.

B) the force on the truck is equal to the force on the car.

4.6 A horizontal force of 200 N is applied to move a 55-kg cart (initially at rest) across a 10 m level surface. What is the final kinetic energy of the cart? A) 4.0 × 103 J B) 2.7 × 103 J C) 1.0 × 103 J D) 2.0 × 103 J

D

4.9 The quantity 1/2 mv2 is A) the potential energy of the object. B) the power supplied to the object by the force. C) the work done on the object by the force. D) the kinetic energy of the object.

D

4.18 A mass on a spring undergoes Simple Harmonic Motion. When the mass is at its maximum displacement from equilibrium, its instantaneous velocity A) is maximum. B) is zero. C) is less than maximum, but not zero. D) cannot be determined from the information given.

A

4.2 If you push twice as hard against a stationary brick wall, the amount of work you do a) remains constant at zero. b) remains constant but non-zero. c) doubles. d) is cut in half.

A

4.8 Matthew pulls his little sister Sarah in a sled on an icy surface (assume no friction), with a force of 60.0 N at an angle of 37.0° upward from the horizontal. 12.0 m, what is the work done by Matthew? A) 575 J B) 720 J C) 433 J D) 185 J

A

2.18 A block of mass M slides down a frictionless plane inclined at an angle θ with the horizontal. The gravitational force is directed A) toward the center of the Earth. B) perpendicular to the plane. C) parallel to the plane in the same direction as the movement of the block. D) parallel to the plane in the opposite direction as the movement of the block

A) toward the center of the Earth.

2.17 A student pulls a box of books on a smooth horizontal floor with a force of 100 N in a direction of 37.0° above the horizontal. If the mass of the box and the books is 40.0 kg, what is the normal force on the box? A)332N B) 292N C) 392N D) 312N

A)332N

2.14 Sue and Sean are having a tug-of-war by pulling on opposite ends of a 5.0-kg rope. Sue pulls with a 15-N force. What is Sean's force if the rope accelerates toward Sue at 2.0 m/s2? A)5.0N B) 25N C) 3.0N D) 50N

A)5.0N

4.10 A 0.200-kg mass attached to the end of a spring causes it to stretch 5.0 cm. If another 0.200-kg mass is added to the spring, the potential energy of the spring will be A) 3 times as much. B) 4 times as much. C) the same. D) twice as much.

B

4.17 If you walk 5.0 m horizontally forward at a constant velocity carrying a 10-N object, the amount of work you do is A) equal to 50 J. B) zero. C) more than 50 J. D) less than 50 J, but more than 0 J.

B

4.5 A 500-kg elevator is pulled upward with a constant force of 5500 N for a distance of 50.0 m. A) -5.20 × 105 J B) 2.75 × 105 J C) 3.00 × 104 J D) -2.45 × 105 J

B

4.12 You slam on the brakes of your car in a panic, and skid a certain distance on a straight, level road. If you had been traveling twice as fast, what distance would the car have skidded, under the same conditions? A) It would have skidded 1.4 times farther. B) It would have skidded twice as far. C) It would have skidded 4 times farther. D) It is impossible to tell from the information given.

C

4.15 A 60-kg skier starts from rest from the top of a 50-m high slope. What is the speed of the slier on reaching the bottom of the slope? (Neglect friction.) A) 22 m/s B) 9.8 m/s C) 31 m/s D) 41 m/s

C

4.3 The area under the curve, on a Force versus position (F vs. x) graph, represents a) potential energy b) kinetic energy. c) work. d) power.

C

4.7 A force moves an object in the direction of the force. The graph in Fig. 6-1 shows the force versus the object's position. Find the work done when the object moves from 0 to 2.0 m. A) 60 J B) 80 J C) 20 J D) 40 J

C

4.4 The quantity Fd/t is a) the potential energy of the object. b) the kinetic energy of the object. c) the work done on the object by the force. d) the power supplied to the object by the force.

D

2.15 During a hockey game, a puck is given an initial speed of 10 m/s. It slides 50 m on the ice before it stops. What is the coefficient of kinetic friction between the puck and the ice? A) 0.11 B) 0.12 C) 0.10 D) 0.090

C) 0.10

3.5 What is the centripetal acceleration of a point on the perimeter of a bicycle wheel of diameter 70 cm when the bike is moving 8.0 m/s? A) 2.1 × 102 m/s2 B) 91 m/s2 C) 1.8×102m/s2 D) 2.7×102m/s2

C) 1.8×102m/s2

2.19 An antitank weapon fires a 3.00-kg rocket which acquires a speed of 50.0 m/s after traveling 90.0 cm down a launching tube. Assuming the rocket was accelerated uniformly, what is the average force acted on it? A)2.00×103N B) 2.82×103N C) 4.17×103N D) 3.62×103N

C) 4.17×103N

3.22 A boy and a girl are riding on a merry-go-round which is turning at a constant rate. The boy is near the outer edge, and the girl is closer to the center. Who has the greater angular speed? A) the boy B) the girl C) Both have the same non-zero angular velocity. D) Both have zero angular velocity.

C) Both have the same non-zero angular velocity. ...BUT... Torri says the answer is B... so take that as you may

2.16 Two boxes of masses m and 2m are connected by a rope. (See Fig.1.) If the forward force on the more massive box is F, what is the acceleration of the less massive box? A) F/(2m) B) F/m C) F/(3m) D) 2F/m

C) F/(3m)

3.17 The Earth orbits the Sun in an elliptical orbit. Ignore any friction which may be present. What happens over time to the Earth's angular momentum about the Sun? A) It continually decreases. B) It remains constant. C) It increases during some parts of the orbit, and decreases during others. D) It continually increases.

C) It increases during some parts of the orbit, and decreases during others.

3.8 What is the SI unit of a spring constant? A) N∙s B) N∙m C) N/m D) N/s

C) N/m

2.4 If you blow up a balloon, and then release it, the balloon will fly away. This is an illustration of A) Newton's second law. B) Galileo's law of inertia. C) Newton's third law. D) Newton's first law.

C) Newton's third law.

3.1 Is it possible for an object moving with a constant speed to accelerate? Explain. A) No, an object can accelerate only if there is a net force acting on it. B) Yes, if an object is moving it can experience acceleration C) Yes, although the speed is constant, the direction of the velocity can be changing. D) No, if the speed is constant then the acceleration is equal to zero.

C) Yes, although the speed is constant, the direction of the velocity can be changing.

2.5 A net force F acts on a mass m and produces an acceleration a. What acceleration results if a net force 2F acts on mass 4m? A)4a B) 8a C) a/2 D) 2a

C) a/2

2.12 An object of mass m is hanging by a string from the ceiling of an elevator. The elevator is moving up at constant speed. What is the tension in the string? A) greater than mg B) less than mg C) exactly mg D) cannot be determined without knowing the speed

C) exactly mg

3.6 A person is standing on a scale in an elevator accelerating downward. Compare the reading on the scale to the person's true weight. A) zero B) equal to their true weight C) less than their true weight D) greater than their true weight downward.

C) less than their true weight

3.18 What is the quantity used to measure an object's resistance to changes in rotation? A) angular velocity B) mass C) moment of inertia D) torque

C) moment of inertia

2.2 In the absence of an external force, a moving object will A) slow down and eventually come to a stop. B) go faster and faster. C) move with constant velocity. D) stop immediately.

C) move with constant velocity.

3.9 A very heavy object moving with speed v collides head-on with a very light object at rest. The collision is elastic, and there is no friction. The heavy object barely slows down. What is the speed of the light object after the collision? A) nearly 2v B) nearly infinite C) nearly v D) nearly 3v

C) nearly v

3.11 Two equal mass balls (one red and the other blue) are dropped from the same height, and rebound off the floor. The red ball rebounds to a higher position. Which ball is subjected to the greater magnitude of impulse during its collision with the floor? A) It's impossible to tell since the time intervals and forces are unknown. B) Both balls were subjected to the same magnitude impulse. C) the red ball D) the blue ball

C) the red ball

2.1 When you sit on a chair, the resultant force on you is A) down. B) depending on your weight. C) zero. D) up.

C) zero.

4.1 What is the correct unit of work expressed in SI units? A)kg m2/s B) kg m/s2 C) kg2 m/s2 D) kg m2/s2

D

4.11 The quantity mgh is A) the power supplied to the object by the force. B) the kinetic energy of the object. C) the work done on the object by the force. D) the gravitational potential energy of the object.

D

4.13 A roller coaster starts from rest at a point 45 m above the bottom of a dip (See Fig. 6-2). Neglect friction, what will be the speed of the roller coaster at the top of the next slope, which is 30 m above the bottom of the dip? A) 24 m/s B) 14 m/s C) 30 m/s D) 17 m/s

D

4.14 Car J moves twice as fast as car K, and car J has half the mass of car K. The kinetic energy of car J, compared to car K is A) the same. B) 1 to 2. C) 4 to 1. D) 2 to 1.

D

4.16 Does the centripetal force acting on an object do work on the object? A) Yes, since a force acts and the object moves, and work is force times distance. B) No, because the object has constant speed. C) Yes, since it takes energy to turn an object. D) No, because the force and the displacement of the object are perpendicular.

D

2.9 The acceleration due to gravity is lower on the Moon than on Earth. Which of the following is true about the mass and weight of an astronaut on the Moon's surface, compared to Earth? A) Mass is less, weight is same. B) Both mass and weight are the same. C) Both mass and weight are less. D) Mass is same, weight is less.

D) Mass is same, weight is less.

2.8 You are standing in a moving bus, facing forward, and you suddenly fall forward as the bus comes to an immediate stop. What force caused you to fall forward? A) normal force due to your contact with the floor of the bus B) gravity C) force due to friction between you and the floor of the bus D) There is not a force leading to your fall.

D) There is not a force leading to your fall.

2.10 Mass and weight A) both measure the same thing. B) are both measured in kilograms C) are exactly equal. D) are two different quantities.

D) are two different quantities.

3.3 What force is needed to make an object move in a circle? A) weight B) kinetic friction C) static friction D) centripetal force

D) centripetal force

2.11 Your bat hits the ball pitched to you with a 1500-N instantaneous force. The ball hits the bat with an instantaneous force, whose magnitude is A) somewhat less than 1500 N. B) essentially zero. C) somewhat greater than 1500 N. D) exactly equal to 1500 N.

D) exactly equal to 1500 N.

3.12 Angular velocity is expressed in units of A) meters per second. B) arcs per second. C) omegas per second. D) radians per second.

D) radians per second.