Phy Test 2 Chapters 6-8

The rectangular board in the figure below is fixed but free to rotate about point P. Forces of equal magnitude are applied to the board at the locations shown in Cases 1-4. ____ Refer to Exhibit 8-2. In which case is the magnitude of the torque on the board the greatest? a. 1 b. 2 c. 3 d. 4

a. 1

How fast would an 80-kg person need to run to have the same momentum as an 18-wheeler (m = 24,000 kg) rolling along at 1 mph? a. 300 mph b. 3000 mph c. 1,920 mph d. 1,920,000 mph

a. 300 mph

When a star undergoes a supernova explosion, the total energy of the universe a. does not change. b. increases. c. decreases.

a. does not change.

A clay ball and a rubber ball have equal mass. A student releases each ball from rest at the same height. The clay ball sticks to the ground while the rubber ball bounces back up. The magnitude of the impulse delivered to the rubber ball by the floor is a. greater than that delivered to the clay ball by the floor b. less than that delivered to the clay ball by the floor c. equal to that delivered to the clay ball by the floor

a. greater than that delivered to the clay ball by the floor

At your new job as youth coordinator in Bozeman, MT, you have been asked to design a midwinter sledding competition. Each competing child pushes a sled along a level, smooth surface for 5 meters. Little Mary Francis brings a sled that is much lighter than all the others. ____ Refer to Exhibit 7-2. Suppose the rules were changed so that the children pushed for a fixed time of 5 seconds rather than a fixed distance of 5 meters. Assuming that each child exerts the same net force, the speed of Mary Francis' sled will be a. greater than that of the others b. less than that of the others c. equal to that of the others d. there is not enough information to determine this

a. greater than that of the others

A solid disk and a hoop have the same mass and radius. Which has the larger rotational inertia about its center of mass? a. hoop b. disk c. They are the same.

a. hoop

An object has a velocity toward the south. If a force directed toward the south acts on the object, it will initially cause the kinetic energy of the object to ____. a. increase b. decrease c. remain the same

a. increase

The rotational inertia of an object increases as the mass ____ and the distance of the mass from the center of rotation ____. a. increases ... increases b. increases ... decreases c. decreases ... increases d. decreases ... decreases

a. increases ... increases

The balancing child on the pedestal in the diagram below is able to stay upright because the center of mass is a. located below the top of the pedestal. b. located at the knees of the child. c. located at the center of the child. d. not important. It is the total mass that determines whether the child stays upright

a. located below the top of the pedestal.

We can explain the recoil that occurs when a rifle is fired by using the conservation of a. momentum. b. kinetic energy. c. work. d. mass.

a. momentum.

The rotational speed of the Earth is slowing because of the tidal influences of the Sun and the Moon. The angular velocity vector of the Earth a. points out of the Earth's north pole. b. points out of the Earth's south pole. c. is zero.

a. points out of the Earth's north pole.

Two objects have different masses but the same momenta. If you stop them with the same retarding force, which one will stop in the shorter distance? a. the heavier one b. the lighter one c. Both stop in the same distance.

a. the heavier one

Newton's first and second laws for translational motion refer to the net force acting on an object. What is the rotational analog of this force? a. torque b. inertia c. acceleration d. force

a. torque

You have been asked to analyze a collision at a traffic intersection. You would be better off a. using conservation of momentum, because kinetic energy was probably not conserved during the collision b. using conservation of momentum, because while kinetic energy was conserved, it is difficult to make the equation for kinetic energy conservation work out c. using conservation of kinetic energy, because momentum was probably not conserved during the collision d. using conservation of kinetic energy, because while momentum was conserved, it is difficult to make the equation for momentum conservation work out

a. using conservation of momentum, because kinetic energy was probably not conserved during the collision

A tennis ball on the end of a string travels in a horizontal circle at a constant speed. The circle has a circumference of 2 m, the ball has a speed of 3 m/s, and the centripetal force is 1.5 N. How much work is done on the ball each time it goes around? a. zero b. 6 J c. 9 J d. 12 J

a. zero

What is the rotational speed of the hand on a clock that measures the minutes? a. 0.000278 rad/s b. 0.00175 rad/s c. 0.0167 rad/s d. 0.105 rad/s

b. 0.00175 rad/s

Two children with masses of 20 and 30 kg are sitting on a balanced seesaw. If the lighter child is sitting 3 m from the center, how far from the center is the heavier child sitting? a. 1 m b. 2 m c. 3 m d. 5 m

b. 2 m

A 20-N block lifted straight upward by a hand applying a force of 20 N has an initial kinetic energy of 26 J. If the block is lifted 1 m, what is the block's final kinetic energy? a. 6 J b. 26 J c. 40 J d. 46 J

b. 26 J

How much energy is required to light a 100-W bulb for 5 h? a. 2500 W-h b. 500 W-h c. 100 W-h d. 20 W-h

b. 500 W-h

Which has the greater kinetic energy, an 18-wheeler parked at the curb or a Volkswagen rolling down a hill? a. 18-wheeler b. Volkswagen c. The kinetic energies are equal.

b. Volkswagen

Under what conditions is the kinetic energy conserved in a collision? a. It is always conserved. b. When the collision is totally elastic. c. When there is no net outside force. d. When there is no friction.

b. When the collision is totally elastic.

If Earth's orbit were circular, each of the following physical quantities would be conserved. For an elliptical orbit only ____ is conserved. a. speed b. angular momentum c. kinetic energy d. size of the linear momentum

b. angular momentum

At which point in the swing of an ideal pendulum (ignoring friction) is the kinetic energy a maximum? a. at either end b. at the lowest point c. It's always the same.

b. at the lowest point

An astronaut "floating" in Skylab has an initial rotational motion but no initial translational motion relative to Skylab. She continues to rotate a. because she experiences no net force. b. because the net force acts through her center of mass. c. because she is weightless. d. because she experiences a torque due to the force of gravity.

b. because the net force acts through her center of mass.

What kind of motion does a constant, non-zero torque produce on an object mounted on an axle? a. constant rotational speed b. constant rotational acceleration c. increasing rotational acceleration d. decreasing rotational acceleration

b. constant rotational acceleration

You are looking from the side at a Ferris wheel and observe that it is rotating clockwise. The direction of the rotational velocity of the Ferris wheel is a. directly toward you. b. directly away from you. c. zero.

b. directly away from you.

A fully-loaded trailer truck is less stable than a race car because the truck a. is more massive. b. has a higher center of mass. c. has bigger wheels. d. weighs more.

b. has a higher center of mass.

Linear momentum is defined to be a. mass times speed. b. mass times velocity. c. mass times acceleration. d. weight times velocity.

b. mass time velocity

Kinetic energy is defined to be one-half the a. mass times the speed. b. mass times the speed squared. c. mass times the acceleration. d. weight times the speed squared.

b. mass times the speed squared.

In physics, work is defined as the product of the a. net force and the distance traveled. b. net force parallel to the motion and the distance traveled. c. net force parallel to the motion and the time it is applied. d. applied force and the distance traveled.

b. net force parallel to the motion and the distance traveled.

A change in the rotational velocity of an object is produced by a net a. force. b. torque. c. rotational inertia. d. moment arm.

b. torque.

How much work is performed by the gravitational force F on a synchronous satellite during one day? a. zero, because the satellite does not move. b. zero, because the force is perpendicular to the velocity. c. FC, where C is the circumference of the orbit. d. Fr, where r is the radius of the orbit

b. zero, because the force is perpendicular to the velocity.

Which has the greater momentum, a heavy truck at rest or a moving roller skate? a. Cannot tell from the information given. b. the heavy truck c. the roller skate d. The momenta are equal.

c. the roller skate

A 1200-kg frictionless roller coaster starts from rest at a height of 20 m. What is its kinetic energy when it goes over a hill that is 10 m high? a. 12,400 J b. 24,000 J c. 120,000 J d. 240,000 J

c. 120,000 J

If a 60-kg sprinter can accelerate from a standing start to a speed of 10 m/s in 2 s, what average power is generated? a. 600 W b. 1200 W c. 1500 W d. 3000 W

c. 1500 W

If a phonograph turntable takes 2 s to reach its rotational speed of 45 rpm, what is its average acceleration? a. 2 rpm/s b. 11.2 rpm/s c. 22.5 rpm/s d. 45 rpm/s

c. 22.5 rpm/s

If a 0.5-kg ball is dropped from a height of 6 m, what is its kinetic energy when it hits the ground? a. 3 J b. 9 J c. 30 J d. There is not enough information to say.

c. 30 J

What is the kinetic energy of an 80-kg sprinter running at 9 m/s? a. 360 J b. 720 J c. 3240 J d. 6480 J

c. 3240 J

If a ball with a weight of 30 N hangs from the end of a 1.5-m horizontal pole, what torque is produced? a. 20 N·m b. 30 N·m c. 45 N·m d. 60 N·m

c. 45 N·m

Which of the following will cause the largest change in the momentum of an object? A force of ____ acting for ____. a. 3 N ... 6 s b. 4 N ... 5 s c. 5 N ... 5 s d. 6 N ... 3 s

c. 5 N ... 5 s

How fast would you have to throw a baseball (m = 145 g) to give it the same momentum as a 10-g bullet traveling at 800 m/s? a. 0.55 m/s b. 1.8 m/s c. 55 m/s d. 800 m/s

c. 55 m/s

A 3-kg toy car with a speed of 6 m/s collides head-on with a 2-kg car traveling in the opposite direction with a speed of 4 m/s. If the cars are locked together after the collision with a speed of 2 m/s, how much kinetic energy is lost? a. 10 J b. 28 J c. 60 J d. 70 J

c. 60 J

The block of wood shown below can be laid face down on any of the three marked faces. Face B is narrower than face A. Which would you put face down to get the least stable position? a. A b. B c. C

c. C

Assuming that your author jumps off the roof of a garage and lands on the ground, how will the impulse the ground exerts on him if he lands on grass compare to that if he lands on concrete? a. The impulse will be larger if he lands on concrete. b. The impulse will be larger if he lands on grass. c. The impulses will be the same independent of the surface

c. The impulses will be the same independent of the surface

Under what conditions is energy conserved? a. When the system is closed to the flow of matter. b. When the system is closed to the flow of energy. c. When the system is closed to the flow of matter and energy. d. Never

c. When the system is closed to the flow of matter and energy.

Under what conditions is the total angular momentum of a system conserved? a. It is always conserved. b. When there is no net outside force. c. When there is no net outside torque. d. When the kinetic energy is also conserved.

c. When there is no net outside torque.

Newton's second law can be rearranged to show that the ____ is equal to the ____. a. momentum ... impulse b. change in momentum ... change in impulse c. change in momentum ... impulse d. momentum ... change in impulse

c. change in momentum ... impulse

A figure skater is spinning with her arms held straight out. The rotational speed of her fingertips is a. greater than that of her elbows b. less than that of her elbows c. equal to that of her elbows

c. equal to that of her elbows

Despite rules to the contrary, a child stands up in the seat of a moving swing. At the moment the swing is at its low point, the rotational speed of the child's feet is a. greater than that of her head b. less than that of her head c. equal to that of her head

c. equal to that of her head

At your new job as youth coordinator in Bozeman, MT, you have been asked to design a midwinter sledding competition. Each competing child pushes a sled along a level, smooth surface for 5 meters. Little Mary Francis brings a sled that is much lighter than all the others. ____ Refer to Exhibit 7-2. Assuming that each child exerts the same net force, the kinetic energy of Mary Francis' sled will be a. greater than that of the others b. less than that of the others c. equal to that of the others d. there is not enough information to determine this

c. equal to that of the others

Air bags are used by stunt people when they fall off buildings to reduce the ____ that occurs during the collision. a. change in momentum b. impulse c. force d. change in velocity

c. force

If a sports car with a mass of 1000 kg travels down the road with a speed of 30 m/s, its momentum is 30,000 a. kg/(m/s) b. kg·s/m c. kg·m/s d. kg·m2 /s2

c. kg·m/s

What impulse is need to stop a 1200-kg car traveling at 20 m/s? a. 60 N·s b. 240 N·s c. 1200 N·s d. 24,000 N·s

d. 24,000 N·s

If the wheel on a car accelerates from rest at a constant rate of 1.5 rev/s2 , how fast will it be turning after 3 s? a. 1.5 rev/s b. 2 rev/s c. 3 rev/s d. 4.5 rev/s

d. 4.5 rev/s

A meter stick is balanced on a stand. If you place a 50-g mass on one side at a distance of 20 cm from the center, how far from the center would you place a 25-g mass on the other side so that the system balances? a. 10 cm b. 20 cm c. 30 cm d. 40 cm

d. 40 cm

How much work does a 60-kg person do against gravity in walking up a trail that gains 720 m in elevation? a. 12 J b. 780 J c. 43,200 J d. 432,000 J

d. 432,000 J

If a CD player uses electricity at a rate of 15 W, how much energy does it use during an 8-h day? a. 15 J b. 120 J c. 720 J d. 432,000 J

d. 432,000 J

A 1800-kg car is traveling at 30 m/s around a curve with a radius of 120 m. What is the angular momentum of the car? a. 450 kg·m2 /s b. 7,200 kg·m2 /s c. 54,000 kg·m2 /s d. 6,480,000 kg·m2 /s

d. 6,480,000 kg·m2 /s

What is the impulse of a 5 N force acting for 15 s? a. 3 N·s b. 15 N·s c. 20 N·s d. 75 N·s

d. 75 N·s

What change in momentum occurs when a force of 20 N acts for 4 s? a. 5 kg·m/s b. 16 kg·m/s c. 24 kg·m/s d. 80 kg·m/s

d. 80 kg·m/s

We can explain the recoil that occurs when a rifle is fired by using a. conservation of momentum. b. equal and opposite impulses. c. equal and opposite changes in momentum d. Any of the above.

d. Any of the above.

A ball dropped from a height of 10 m only bounces to a height of 5 m. Which of the following statements is valid for this situation? a. Kinetic energy is conserved. b. Mechanical energy is conserved. c. Gravitational potential energy is conserved. d. None of the above.

d. None of the above.

A sports car with a mass of 1000 kg travels down the road with a speed of 20 m/s. Which is larger, its momentum or its kinetic energy? a. momentum b. kinetic energy c. They are equal. d. The two cannot be compared.

d. The two cannot be compared.

An elephant, an ant, and a professor jump from a lecture table. Assuming no frictional losses, which of the following could be said just before they hit the floor? a. They all have the same kinetic energy. b. They all started with the same potential energy. c. They will all experience the same force on stopping. d. They all have the same speed.

d. They all have the same speed.

What is the gravitational potential energy of a ball with a weight of 50 N when it is sitting on a shelf 2 m above the floor? a. 100 J b. 200 J c. 400 J d. We cannot say without knowing the zero level.

d. We cannot say without knowing the zero level.

Power is defined to be the energy a. lost in a process. b. lost in a process divided by the time it takes. c. changed to other forms in a process. d. changed to other forms divided by the time it takes.

d. changed to other forms divided by the time it takes.

The reason a figure skater spins slower as he extends his arms is because a. he experiences a smaller torque. b. his angular momentum is greater. c. his angular momentum is less. d. his rotational inertia is greater.

d. his rotational inertia is greater.

Padded dashboards in automobiles are safer because the a. momentum change is less b. impulse is less c. impact time is less d. impact time is greater

d. impact time is greater

The stunt person who is shot by a bandit and falls from the balcony into an air bag rather than onto the ground will not be hurt because the a. momentum change is less for the air bag. b. momentum is less for the air bag. c. impulse is less for the air bag. d. increased stopping time means a smaller stopping force.

d. increased stopping time means a smaller stopping force.

If a sports car with a mass of 1000 kg travels down the road with a speed of 20 m/s, its kinetic energy is 200,000 a. kg/(m/s)2 b. kg·s2 /m2 c. kg·m/s d. kg·m2 /s2

d. kg·m2 /s2

Which of the following is an energy unit? a. newton b. kilowatt c. kilogram-meter/second d. kilowatt-hour

d. kilowatt-hour

An object's resistance to a change in its rotational velocity is called its a. inertia. b. mass. c. torque. d. rotational inertia

d. rotational inertia

A bowler lifts a bowling ball from the floor and places it on a rack. If you know the weight of the ball, what else must you know in order to calculate the work she does on the ball? a. the mass of the ball b. the time required c. nothing else d. the height of the rack

d. the height of the rack

Assume that a red car has a mass of 1000 kg and a white car has a mass of 2000 kg. If both cars are traveling at the same velocity, a. their kinetic energies are equal. b. their momenta are equal. c. the red car's kinetic energy is twice as big. d. the white car's kinetic energy is twice as big.

d. the white car's kinetic energy is twice as big.

Newton's first law for rotational motion states that an object will maintain its state of rotational motion unless acted on by an unbalanced (or net) a. force. b. velocity. c. inertia. d. torque.

d. torque.

Which of the following is NOT a unit of energy? a. joule b. newton-meter c. kilowatt-hour d. watt

d. watt

Assume that two cars have the same kinetic energy, but that the red car has twice the mass of the blue car. We then know that the speed of the red car is ____ as the blue car. a. one-half as much b. one-fourth as much c. twice as much d. four times as much e. none of these

e. none of these