Exam 2

-28.0 kg∙m2/s k

A 2.00-kg mass is located at r= 2.00i m + 3.00j m and has velocity v = 4.00 m/si - 1.00 m/sj . What is the angular momentum of the mass? 10.0 kg∙m2/s 16.0 kg∙m2/s -6.00 kg∙m2/s -28.0 kg∙m2/s 10.0 kg∙m2/s 20.0 kg∙m2/s

7.1 m/s

A 2.3-kg object traveling at 6.1 m/s collides head-on with a 3.5-kg object traveling in the opposite direction at 4.8 m/s. If the collision is perfectly elastic, what is the final speed of the 2.3-kg object? 3.8 m/s 7.1 m/s 6.6 m/s 4.3 m/s 0.48 m/s

1390 J

A 20-kg object is resting at the top of a table 1.6 m above ground level. The object is then picked up and moved to a height of 8.7 m above ground level. What is the change in the gravitational potential energy of this object? 320 J 71 J 1390 J 140 J 1740 J

-1500 J

A 30 N-force toward the west is applied to an object. The object moves 50 m east during the time the force is applied. What is the change in kinetic energy of the object? 750 J 1.0 J 1.7 J -1500 J 0.0 J

stable equilibrium

A sphere hanging freely from a cord is in unstable equilibrium. negative equilibrium. stable equilibrium. neutral equilibrium. positive equilibrium.

0.308 kg∙m/s upwards

A 0.140-kg baseball is dropped and reaches a speed of 1.20 m/s just before it hits the ground. It rebounds with a speed of 1.00 m/s. What is the change of the ball's momentum? 0 kg∙m/s 0.0280 kg∙m/s upwards 0.308 kg∙m/s upwards 0.308 kg∙m/s downwards 0.0280 kg∙m/s downwards

0.261 rad/s

A 40.0-kg child running at a speed 3.00 m/s jumps on a stationary playground merry-go-round at a distance 1.50 m from the axis of rotation of the merry-go-round. The child is traveling tangential to the edge of the merry-go-round which has a 600 kg∙m2 moment of inertia about its axis of rotation as she is running. What is the angular speed of the merry-go-round after the child jumps on it? 3.14 rev/s 6.28 rev/s 2.00 rad/s 0.788 rad/s 0.261 rad/s

0.40 rad/s

A 5.0-m radius playground merry-go-round with a moment of inertia of 2000 kg∙m2 is rotating freely with an angular speed of 1.0 rad/s. Two people, each having a mass of 60 kg are standing right outside the edge of the merry-go-round and step on it with negligible speed. What is the angular speed of the merry-go-round right after the two people have stepped on? 0.40 rad/s 0.20 rad/s 0.60 rad/s 0.80 rad/s 0.67 rad/s

0.153

A 5.00-kg box slides 3.00 m across the floor before coming to rest. What is the coefficient of kinetic friction between the floor and the box if the box had an initial speed of 3.00 m/s? 0.153 0.306 0.200 1.50 0.587

It loses 0.23 J.

A 620-g object traveling at 2.1 m/s collides head-on with a 320-g object traveling in the opposite direction at 3.8 m/s. If the collision is perfectly elastic, what is the change in the kinetic energy of the 620-g object? It loses 1.4 J. It gains 0.69 J. It loses 0.47 J. It loses 0.23 J. The energy of the object is unchanged.

14 m/s

A car on a roller coaster starts at zero speed at an elevation above the ground of 26 m. It coasts down a slope, and then climbs a hill. The top of the hill is at an elevation of 16 m. What is the speed of the car at the top of the hill? Neglect any frictional effects. 9 m/s 14 m/s 18 m/s 6 m/s 10 m/s

unstable equilibrium.

A cone balanced on its small end is in neutral equilibrium. stable equilibrium. negative equilibrium. unstable equilibrium. positive equilibrium.

The disk

A disk and a hoop of the same mass and radius are released at the same time at the top of an inclined plane and roll without slipping. Which object reaches the bottom of the incline first? The disk The hoop Both reach the bottom at the same time. It depends on the angle of inclination. It depends on the length of the inclined surface.

0.74 rad/s2

A fan is turned off, and its angular speed decreases from 10.0 rad/s to 6.3 rad/s in 5.0 s. What is the magnitude of the angular acceleration of the fan? 0.74 rad/s2 1.16 rad/s2 11.6 rad/s2 0.37 rad/s2 0.86 rad/s2

conservation of angular momentum: her moment of inertia is decreased, and so her angular speed must increase to conserve angular momentum.

A figure skater is spinning slowly with arms outstretched. She brings her arms in close to her body and her angular speed increases dramatically. The speed increase is a demonstration of Newton's second law for rotational motion: she exerts a torque and so her angular speed increases. conservation of kinetic energy: her moment of inertia is decreased, and so her angular speed must increase to conserve energy. conservation of angular momentum: her moment of inertia is decreased, and so her angular speed must increase to conserve angular momentum. conservation of total energy: her moment of inertia is decreased, and so her angular speed must increase to conserve energy. This has nothing to do with mechanics, it is simply a result of her natural ability to perform.

21.2 kg∙m/s at 39.5° from the x-axis

A firecracker breaks up into two pieces, one has a mass of 200 g and flies off along the x-axis with a speed of 82.0 m/s and the second has a mass of 300 g and flies off along the y-axis with a speed of 45.0 m/s. What is the total momentum of the two pieces? 361 kg∙m/s at 0.983° from the x-axis 21.2 kg∙m/s at 56.3° from the x-axis 93.5 kg∙m/s at 28.8° from the x-axis 361 kg∙m/s at 56.3° from the x-axis 21.2 kg∙m/s at 39.5° from the x-axis

40 m/s

A golf club exerts an average force of 1000 N on a 0.045-kg golf ball which is initially at rest. The club is in contact with the ball for 1.8 ms. What is the speed of the golf ball as it leaves the tee? 35 m/s 50 m/s 40 m/s 45 m/s 30 m/s

0.10 m

A linear spring has a spring constant of 20 N/m. How far would it have to be stretched to have a potential energy of 0.10 J? 20 m 0.0050 m 0.10 m 200 m 2.0 m

127 g

A meter stick balances at the 50.0-cm mark. If a mass of 50.0 g is placed at the 90.0-cm mark, the stick balances at the 61.3-cm mark. What is the mass of the meter stick? 127 g 178 g 73.4 g 89.7 g 32.6 g

0 J

A person carries a mass of 10 kg and walks along the +x-axis for a distance of 100m with a constant velocity of 2 m/s. What is the work done by this person? 20 J 0 J 1000 J 200 J None of the other choices is correct.

her moment of inertia increases and her angular velocity decreases.

A person sits on a freely spinning lab stool (no friction). When this person extends her arms, her moment of inertia increases and her angular velocity decreases. her moment of inertia decreases and her angular velocity decreases. her moment of inertia increases and her angular velocity increases. her moment of inertia decreases and her angular velocity increases. her moment of inertia increases and her angular velocity remains the same.

moves along a parabolic path.

A plane, flying horizontally, releases a bomb, which explodes before hitting the ground. Neglecting air resistance, the center of mass of the bomb fragments, just after the explosion moves along a parabolic path. is zero. moves vertically. moves horizontally.

221.4° from the x-axis

A plate falls vertically to the floor and breaks up into three pieces, which slide along the floor. Immediately after the impact, a 200-g piece moves along the x-axis with a speed of 2.00 m/s and a 235-g piece moves along the y-axis with a speed of 1.50 m/s. The third piece has a mass of 100 g. In what direction does the third piece move? 41.4° from the x-axis 221.4° from the x-axis 36.9° from the x-axis 216.9° from the x-axis 39.9° from the x-axis

1.6 rad/s

A playground merry-go-round with a radius of 2.0 m and a rotational inertia of 100 kg m2 is rotating at 3.0 rad/s. A child with a mass of 22 kg jumps onto the edge of the merry-go-round, traveling radially inward. What is the new angular speed of the merry-go-round? 1.2 rad/s 1.6 rad/s 3.4 rad/s 2.4 rad/s 2.0 rad/s

0.092 J

A solid cylinder with a radius of 10 cm and a mass of 3.0 kg is rotating about its center with an angular speed of 3.5 rad/s. What is its kinetic energy? 1.05 J 0.96 J 0.53 J 0.18 J 0.092 J

21.1 revolutions per second

A uniform 2.00-kg circular disk of radius 20.0 cm is rotating clockwise about an axis through its center with an angular speed 30.0 revolutions per second. A second uniform 1.50-kg circular disk of radius 15.0 cm that is not rotating is dropped onto the first disk so that the axis of rotation of the first disk passes through the center of the second disk. What is the final angular speed of the two disks when they are rotating together? 12.7 revolutions per second 21.1 revolutions per second 16.9 revolutions per second 17.1 revolutions per second 19.2 revolutions per second

2.1 m

A uniform 40-N board supports two children weighing 500 N and 350 N. If the support is at the center of the board and the 500-N child is 1.5 m from its center, how far is the 350-N child from the center? 1.5 m 2.7 m 1.1 m 2.1 m

1.6 m

A uniform beam with a mass of 120 kg and a length of 5.0 m rests on two supports, one at the left edge and one 3.0 m from the left edge. How close to the right edge can a 68-kg person walk along the beam without causing it to tip over? 1.5 m 0.50 m 0.88 m 1.8 m 1.6 m

948 rad

A wheel that is rotating at 33.3 rad/s is given an angular acceleration of 2.15 rad/s2. Through what angle has the wheel turned when its angular speed reaches 72.0 rad/s? 697 rad 316 rad 83.2 rad 948 rad 66.8 rad

11.3 N∙m

A wrench is acting on a nut. The length of the wrench lies directly to the east of the nut. A force 150 N acts on the wrench at a position 15.0 cm from the center of the nut in a direction 30.0° north of east. What is the torque about the center of the nut? 11.3 N∙m 22.5 N∙m 2250 N∙m 1949 N∙m 19.5 N∙m

0.33

An 8.0 kg object moving with an initial velocity of 8.0 m/s on a surface comes to rest due to friction after it travels a horizontal distance of 10 m. What is the coefficient of kinetic friction between the object and the surface? 0.33 0.25 0.80 0.43 0.13

the net torque is not zero.

Angular momentum cannot be conserved if there is a net force on the system. the net torque is not zero. the angular velocity changes. the angular acceleration changes. the moment of inertia changes.

3 cm

At what speed must a 150-kg football player be moving to have the same momentum as a 15.0-g bullet traveling at 300 m/s? 30.0 m/s 3.00 cm/s 1.00 m/s 3.00 m/s 10.0 m/s

block 2 is faster

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? We must know the actual masses of the blocks to answer. Both blocks have the same speed at the bottom. Block 1 is faster. Block 2 is faster. There is not enough information to answer the question.

Translational kinetic energy is larger.

Consider a solid sphere of radius R and mass M rolling without slipping. Which form of kinetic energy is larger, translational or rotational? Rotational kinetic energy is larger. Translational kinetic energy is larger. Both are equal. You need to know the speed of the sphere to tell. You need to know the acceleration of the sphere to tell.

decreases

If the net work done on an object is negative, then the object's kinetic energy increases. decreases. remains the same. is zero. cannot be determined without knowing the object's mass.

false

If the sum of both the external torques and the external forces on an object is zero, then the object must be at rest. True False

false

If the sum of the external torques on an object is zero, then the sum of the external forces on it must also be zero. True False

7500 N/m

If the work done to stretch a spring by 4.0 cm is 6.0 J, what is the spring constant? 300 N/m 6000 N/m 7500 N/m 3000 N/m 3500 N/m

If you push twice as hard against a stationary brick wall, the amount of work you do

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

340 N m

In an effort to loosen the bolt on the wheel of a car, a man with a mass of 70 kg steps on the end of a 50-cm tire iron which is extending horizontally from the bolt. How much torque is he applying to the bolt? 35 N m 340 N m 140 N m 70 N m 14 N m

The stone's kinetic energy decreases while its gravitational potential energy increases.

Neglecting air resistance, when you toss a stone straight up in the air from Earth's surface, which of the following statements is true for the upward motion of the stone. The stone's kinetic energy decreases while its gravitational potential energy increases. The stone's kinetic and gravitational potential energies increase simultaneously. The stone's kinetic energy increases while its gravitational potential energy decreases. The stone's kinetic and gravitational potential energies decrease simultaneously. The stone's total energy increases.

The object's center of mass will not move, but the object may begin to rotate.

Several forces act on an object at rest. It is known that the sum of the forces acting on the object is zero. Which statement is necessarily true? The object's center of mass may accelerate, but the object will remain in the same orientation. The object's center of mass may move in such a way that the object will roll without slipping. The object will remain stationary. The object's center of mass will not move, but the object may begin to rotate. The object's center of mass may accelerate and the object may begin to rotate.

the ratio of the change in length to the original length.

Strain is the same as force. the ratio of the change in length to the original length. the ratio of stress to elastic modulus. the applied force per cross-sectional area. the stress per unit area.

v1 = v2

Swimmers at a water park have a choice of two frictionless water slides (see Fig. 8-3). Although both slides drop over the same height, h, slide 1 is straight while slide 2 is curved, dropping quickly at first and then leveling out. How does the speed v1 of a swimmer reaching the end of slide 1 compares with v2, the speed of a swimmer reaching the end of slide 2? v1 < v2 v1 = v2 v1 > v2 No simple relationship exists between v1 and v2.

may be changing.

The total force on an object is zero. The angular momentum of the object can only be changing direction. may be changing. can only be changing magnitude. is zero. is constant.

0J

Three applied forces, 1 = 20.0 N, 2 = 40.0 N, and 3 = 10.0 N, act on an object with a mass of 2.00 kg which can move along an inclined plane as shown in the figure. The questions refer to the instant when the object has moved 0.600 m along the surface of the inclined plane in the upward direction. Neglect friction and use g = 10.0 m/s2.Refer to Fig. 7-2. What is the amount of work done by the force 3 as the object moves up the inclined plane? 20.8 J 0 J 24.0 J 16.0 J 12.0 J

20.8 J

Three applied forces, F1 = +20.0 N, F2 = +40.0 N, and F3 = 10.0 (perpendicular) N, act on an object with a mass of 2.00 kg which can move along an inclined plane as shown in the figure. The questions refer to the instant when the object has moved 0.600 m along the surface of the inclined plane in the upward direction. Neglect friction and use g = 10.0 m/s2.Refer to Fig. 7-2. What is the amount of work done by force 2 as the object moves up the inclined plane? 16.0 J 12.0 J 24.0 J 0 J 20.8 J

They have the same non-zero angular displacement.

Two children are riding on a merry-go-round. Child A is at a greater distance from the axis of rotation than child B. Which child has the larger angular displacement? Child A Child B They have the same zero angular displacement. They have the same non-zero angular displacement. There is not enough information given to answer the question.

Child A

Two children are riding on a merry-go-round. Child A is at a greater distance from the axis of rotation than child B. Which child has the larger linear displacement? Child A Child B They have the same non-zero linear displacement. They have the same zero linear displacement. There is not enough information given to answer the question

Neither of them do any work.

Two men, Joel and Jerry, push against a wall. Jerry stops after 10 min, while Joel is able to push for 5.0 min longer. Compare the work they do. Joel does 75% more work than Jerry. Jerry does 50% more work than Joel. Joel does 25% more work than Jerry. Joel does 50% more work than Jerry. Neither of them do any work.

to your left

When you ride a bicycle, in what direction is the angular velocity of the wheels? to your right to your left backwards up forwards

It would have skidded 4 times farther

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? It would have skidded 1.4 times farther. It would have skidded one half as far. It would have skidded 4 times farther. It would have skidded twice as far. It is impossible to tell from the information given.

The final momentum is zero kg∙m/s but the final kinetic energy is positive.

acques and George meet in the middle of a lake while paddling in their canoes. They come to a complete stop and talk for a while. When they are ready to leave, Jacques pushes George's canoe with a force F to separate the two canoes. What is correct to say about the final momentum and kinetic energy of the system? The final momentum is zero kg∙m/s but the final kinetic energy is positive. The final momentum is in the direction of and the final kinetic energy is positive. The final momentum is in the direction of but the final kinetic energy is zero J. The final momentum is in the direction opposite of but the final kinetic energy is zero J. The final momentum is zero kg∙m/s and the final kinetic energy is zero J.

lowest point

highest speed at.. (parabola)

lowest point

most KE (parabola)

highest point

most PE (parabola)