Mechanics Review mc questions 2014 - Weebly

The net force on a moving object is suddenly reduced to zero. As a consequence, the object

(A) stops abruptly (B) stops during a short time interval (C) changes direction (D) continues at a constant velocity (E) changes velocity in an unknown manner

5 m

2 m

5 m

2 m

A 5 m uniform plank of mass 100 kg rests on the top of a building with 2 m extended over the edge as

shown above. How far can a 50-kg person venture past the edge of the building on the plank before the plank just begins to tip?

(A) 0.5 m (B) 1.0 m (C) 1.5 m (D) 2.0 m (E) It is impossible to make the plank tip since the person would have to be more than 2 meters from

the edge of the building.

An astronomer estimates the mass of galaxy 1 to be 1011 solar masses. Galaxy 2 has a mass one-third that

of galaxy 1. Which of the following is the best order of magnitude estimate for the mass of the galaxy 2?

(A) 103 solar masses (B) 105 solar masses (C) 108 solar masses (D) 1011 solar masses (E) 1014 solar masses

2 kg12 N

15 N

A block of mass 2 kg slides along a horizontal tabletop. A horizontal applied force of 12 N and a vertical

applied force of 15 N act on the block, as shown above. If the coefficient of kinetic friction between the block and the table is 0.2, the frictional force exerted on the block is most nearly

(A) 1 N (B) 3 N (C) 4 N (D) 5 N (E) 7 N

Consider the figure above which shows a ball that is projected and follows a parabolic path. Point Y is the

highest point on the path, and air resistance is negligible. Which of the following best shows the direction of the acceleration of the ball at point X?

(A) (D)

(B)

(E)

(C)

X Y

x

t

AB

C DE

The motion of a particle along a straight line is represented by the position, x, versus time, t, graph above.

At which of the labeled points on the graph is the magnitude of the acceleration of the particle greatest?

(A) A (B) B (C) C (D) D (E) E

xCv 21

2 2=

In the above equation, the distance x is measured in meters, the time t is in seconds, and the velocity v is in meters per second. What are the SI units of the constant C1 ?

(A) m

(B) sm

(C) m/s2 (D) m

(E) m2

A massless rigid rod of length 3d is pivoted at a fixed point W, and two forces each of magnitude F are

applied vertically upward as shown above. A third vertical force of magnitude F may be applied, either upward or downward, at one of the labeled points. With the proper choice of direction at each point, the rod can be in equilibrium if the third force of magnitude F is applied at point

(A) W only (B) Y only (C) V or X only (D) V or Y only (E) V, W, or X

An airplane heads due east at 600 km/hr. The wind blows from the north at 150 km/hr. The cardinal

directions (N, S, E, W) are represented as indicated below. With respect to the earth, the plane’s velocity is best represented by which vector?

Three forces act on an object. If the object is in translational equilibrium, which of the following must be true?

I. The vector sum of the three forces must equal zero. II. The magnitudes of the three forces must be equal III. All three forces must be parallel

(A) I only (B) II only (C) I and III only (D) II and III only (E) I, II, and III

velocity(m/s)

2

1

time (s)1 2 3 4 65

3

4

5

6

An object of mass 2 kg moves according to the velocity-time graph pictured above. The net force on the

object from 0 to 4 seconds is

(A) –2.7 N (B) –2.0 N (C) 0 (D) +2.0 N (E) +2.7 N

37o

5 m

4 m

3 m

A 2 kg block sits at rest on the incline shown above. The magnitude of the normal force exerted on the

block by the plane is most nearly

(A) 10 N (B) 12 N (C) 16 N (D) 20 N (E) 33 N

Questions 1-2 relate to five particles that start at position x = 0 at time t = 0 and move in one dimension independently of one another. Graphs of the velocity of each particle versus time are shown below. v (m/s)

1

0

-1

time (s)

1 2

Particle A

v (m/s)

1

0

-1

time (s)

1 2

Particle B v (m/s)

1

0

-1

time (s)

1 2

Particle C

v (m/s)

1

0

-1

time (s)

1 2

Particle D v (m/s)

1

0

-1

time (s)

1 2

Particle E Which particle is farthest from the origin at t = 2 seconds?

(A) A (B) B (C) C (D) D (E) E

Which particle moves with a constant nonzero acceleration?

(A) A (B) B (C) C (D) D (E) E

The figure above shows a cart of mass M accelerating to the right with a block of mass m held to the front

surface only by friction. The coefficient of friction between the surfaces is µ. What is the minimum acceleration a of the cart such that the block will not fall?

A stone of mass 1 kg and weight 10 N falls through the air. The air resistance acting on the stone is 2 N.

What is the acceleration of the stone?

(A) 12 m/s2 (B) 9.8 m/s2 (C) 8 m/s2 (D) 5 m/s2 (E) 2 m/s2

A massless rod is supported at point P as shown above. A block weighing 40 N is attached to the rod 0.2 m from P. How far from point P must a block weighing 80 N be attached in order to balance the rod?

(A) 0.1 m (B) 0.2 m (C) 0.4 m (D) 0.5 m (E) 0.8 m

A horizontal force F is used to pull a 5-kg block across a floor at a constant speed of 3 m/s. The frictional force

between the block and the floor is 10 N. What is the value of the coefficient of kinetic friction, µk?

(A) 0.10 (B) 0.15 (C) 0.20 (D) 0.25 (E) 0.50

The one of the following that is not a vector is

(A) acceleration (B) force (C) speed (D) velocity (E) momentum

If an object experiences no net force, which of the following must be true about its motion?

I. The object has an average velocity of zero. II. The object's velocity does not change. III. The object cannot move.

(A) I only (B) II only (C) III only (D) I and II only (E) I and III only

A car rounds a curve at a steady 40 m/s. Which of the following is happening to the car’s velocity vector?

(A) It is increasing in magnitude. (B) It is decreasing in magnitude. (C) It does not change. (D) Its magnitude remains constant but its direction changes. (E) Its magnitude is zero.

Two trains, X and Y, begin moving on parallel tracks from the same starting position at a train station. The

graph above shows their respective distances from the starting point as functions of time. At time T, which of the following is true?

(A) Train X is moving faster than train Y. (B) Train Y is moving faster than train X. (C) Trains X and Y are moving at the same speed. (D) Train X is ahead of train Y. (E) Train Y is ahead of train X.

T t

Position Y

X

Consider a system consisting only of the earth and a bowling ball, which moves upward in a parabola 10 m

above earth’s surface. The downward force of earth’s gravity on the ball, and the upward force of the ball’s gravity on the earth, form a Newton’s third law force pair. Which of the following statements about the ball is correct?

(A) The ball must be in equilibrium since the upward forces must cancel downward forces. (B) The ball accelerates toward the earth because the force of gravity on the ball is greater than the force of

the ball on the earth. (C) The ball accelerates toward the earth because the force of gravity on the ball is the only force acting on

the ball. (D) The ball accelerates away from earth because the force causing the ball to move upward is greater than

the force of gravity on the ball. (E) The ball accelerates away from earth because the force causing the ball to move upward plus the force

of the ball on the earth are together greater than the force of gravity on the ball.

A cart is initially moving at 0.5 m/s along a track. The cart comes to rest after traveling 1 m. The experiment

is repeated on the same track, but now the cart is initially moving at 1 m/s. How far does the cart travel before coming to rest?

(A) 1 m (B) 2 m (C) 3 m (D) 4 m (E) 8 m

A wheel of radius R and negligible mass is mounted on a horizontal frictionless axle so that the wheel is in a vertical plane. Three small objects having masses m, M, and 2M, respectively, are mounted on the rim of the wheel, as shown above. If the system is in static equilibrium, what is the value of m in terms of M?

(A) M2

(B) M

(C) 32M

(D) 2M

(E) 52m

A rubber ball bounces on the ground as shown. After each bounce, the ball reaches one-half the height of the bounce before it. If the time the ball was in the air between the first and second bounce was 1 second, what would be the time between the second and third bounce?

(A) 0.50 s (B) 0.71 s (C) 1.0 s (D) 1.4 s (E) 2.0 s

A rock of mass m is thrown horizontally off a building from a height h, as shown above. The speed of the rock as it leaves the thrower's hand at the edge of the building is 0υ . How much time does it take the rock to travel from the edge of the building to the ground?

(A) hυ0 (B) h υ 0 (C) h gυ 0 (D) 2h g (E) 2h g

14. A 20 kg boulder rests on the surface of the Earth, which has a mass of 5.98 x 1024 kg. What is the

magnitude of the gravitational force that the boulder exerts on Earth?

(A) 5.98 x 1025 N (B) 5.98 x 1024 N (C) 200 N (D) 20 N (E) The boulder exerts no force on the earth.

Which of the above graphs could correctly represent the motion of an object moving with a constant speed in a straight line?

(F) graph I only (G) graph II only (H) graphs I and IV only (I) graphs II and V only (J) All of the above graphs represent constant speed in a straight line.

Three stones of different mass (1m, 2m, and 3m) are thrown vertically upward with different velocities (1v, 2v, and 3v, respectively). The diagram indicates the mass and velocity of each stone. Rank from high to low the maximum height of each stone. Assume air resistance is negligible.

(K) [high] I, II, III [low] (L) [high] II, I, III [low] (M) [high] III, II, I [low] (N) [high] I, III, II [low] (O) All reach the same height.

Is it possible for an object’s velocity to increase while its acceleration decreases?

(P) No, this is impossible because of the way in which acceleration is defined. (Q) No, because if acceleration is decreasing the object will be slowing down. (R) No, because velocity and acceleration must always be in the same direction. (S) Yes, an example would be an object falling near the surface of the moon. (T) Yes, an example would be an object falling in the presence of air resistance.

Above is velocity-time graph representing a duck flying south for the winter. At what point did the duck stop its forward motion?

(A) A (B) B (C) C (D) D (E) Between A and B

A block rests on an incline that makes an angle θ with the horizontal. The block remains at rest as θ is slowly increased. What happens to the magnitudes of the normal force and the static friction force of the incline on the block?

a. Both increase b. Both decrease c. Both remain the same d. The normal force increases while the friction force decreases. e. The friction force increases while the normal force decreases.

Two boxes are accelerated to the right on a frictionless horizontal surface as shown above. The larger box has a mass of 9 kg, and the smaller box has a mass of 3 kg. If a 24 N horizontal force pulls on the larger box, with what force does the larger box pull on the smaller box?

(A) 3 N (B) 6 N (C) 8 N (D) 18 N (E) 24 N

A toy car moves along the x-axis according to the velocity-time graph shown above. When does the car have zero acceleration?

f. At 2.0 and 4.0 seconds g. At 3.0 seconds h. At 3.3 and 5.1 seconds i. The acceleration is always zero. j. The acceleration is never zero.

A ball of mass m is thrown horizontally at a vertical wall with a speed v and bounces off elastically and

horizontally. What is the magnitude of the change in momentum of the ball? (A) 2mv (B) mv (C) zero

(D) 4mv

(E) 2mv

A solid metal ball and a hollow plastic ball of the same external radius are released from rest in a large vacuum chamber. When each has fallen 1 m, they both have the same

(A) inertia (B) speed (C) momentum (D) kinetic energy (E) change in potential energy

If a ball is thrown directly upwards with twice the initial speed of another, how much higher will it be at its apex?

(A) 8 times (B) 4 times (C) 22 times (D) 2 times (E) 2 times

1. Which one of the following quantities can have its

unit expressed as 2smkg ⋅

?

(A) force (B) power (C) kinetic energy (D) pressure (E) linear momentum

2. Consider the motion of an object described by the

position-time graph above. For what time(s) is the speed of the object the greatest? (A) At all times from t = 0 s to t = 2.0 s (B) At time t = 3.0 s (C) At time 4.0 s (D) At all times from t = 5.0 s to 7.0 s (E) At time t = 8.5 s

3. A car with mass M initially travels to the east with speed 4v. A truck initially travels to the west with speed 3v. After the vehicles collide, they move together to the west with common speed 2v. What is the mass of the truck?

(A) 2M (B) 3M (C) 4M (D) 5M (E) 6M

4. A 5.0 kg solid sphere falls at more than its terminal

velocity near the surface of the earth. The mass of the earth is 6.0 x 1024 kg. What is the magnitude of the gravitational force exerted by the solid sphere on the earth? (A) 0 N (B) 5 N (C) 50 N (D) 6 x 1025 N (E) It is immeasurably small, but not zero.

5. The free fall trajectory of an object thrown from the

top of a building is shown as the dashed line in the figure above. Which sets of arrows best correspond to the directions of the velocity and of the acceleration for the object at the point labeled P on the diagram?

6. In the velocity-time graph above, the positive

direction is east. Which of the following is correct? (A) The object moves to the west the entire time. (B) The object moves to the east the entire time. (C) The object moves to the west, and then to the

east. (D) The object moves to the east, and then to the

west. (E) The object changes its direction of motion more

than once.

7. A 10 kg box remains at rest while a person pushes

directly to the right on the box with a force of 60 N. The coefficient of kinetic friction between the box and the surface is µk = 0.20. The coefficient of static friction between the box and the surface is µs = 0.60. What is the magnitude of the force of friction acting on the box during the push?

(A) 200 N (B) 120 N (C) 60 N (D) 40 N (E) 0 N

8. A point object is connected to the end of a long

string of negligible mass and the system swings as a simple pendulum with period T. What is the period of the pendulum if the string is made to have one-quarter of its original length?

(A) 4T (B) 2T (C) T (D) T / 2 (E) T / 4

9. A mass m is pulled outward until the string of length

L to which it is attached makes a 90o angle with the vertical. The mass is released from rest and swings through a circular arc. What is the tension in the string when the mass swings through the bottom of the arc?

(A) 0 (B) ½mg (C) mg (D) 2mg (E) 3mg

10. Two boxes of different masses in an orbiting space station appear to float at rest – one above the other – with respect to the station. An astronaut applies the same force to both boxes. Can the boxes have the same acceleration with respect to the space station?

(A) No, because the boxes are moving in orbits of

different radius. (B) No, because the box of greater mass requires

more force to reach the same acceleration. (C) Yes, because both boxes appear weightless. (D) Yes, because both boxes are accelerating toward

earth at the same rate. (E) It cannot be determined without knowing

whether the boxes are being pushed parallel or perpendicular to earth’s gravity.

11. An object is dropped from rest from a certain height.

Air resistance is negligible. After falling a distance d, the object’s kinetic energy is proportional to which of the following?

(A) 21d

(B) d1

(C) d (D) d (E) 2d

12. An object is projected vertically upward from ground

level. It rises to a maximum height H. If air resistance is negligible, which of the following must be true for the object when it is at height H/2?

(A) Its speed is half of its initial speed. (B) Its kinetic energy is half of its initial kinetic

energy. (C) Its potential energy is half of its initial potential

energy. (D) Its total mechanical energy is half of its initial

value. (E) Its total mechanical energy is half of its value at

the highest point.

13. A boy of mass m and a girl of mass 2m are initially

at rest at the center of a frozen pond. They push each other so that she slides to the left at speed v across the frictionless ice surface and he slides to the right as shown above. What is the total work done by the children?

(A) Zero (B) mv (C) mv2 (D) 2mv2 (E) 3mv2

14. An object of mass M travels along a horizontal air

track at a constant speed v and collides elastically with an object of identical mass that is initially at rest on the track. Which of the following statements is true for the two objects after the impact?

(A) The total momentum is Mv and the total kinetic

energy is ½Mv2. (B) The total momentum is Mv and the total kinetic

energy is less than ½Mv2. (C) The total momentum is less than Mv and the total

kinetic energy is ½Mv2. (D) The momentum of each object is ½Mv. (E) The kinetic energy of each object is ¼Mv2.

15. A spherical planet has mass greater than that of

earth, but its density is unknown. The weight of an object on that planet compared with its weight on earth is which of the following?

(A) Larger (B) The same (C) Smaller (D) It cannot be determined without information

about the planet’s size. (E) It cannot be determined without information

about the planet’s atmosphere.

16. A 2 kg object initially moving with a constant

velocity is subjected to a force of magnitude F in the direction of motion. A graph of F as a function of time t is shown above. What is the increase, if any, in the velocity of the object during the time the force is applied?

(A) 0 m/s (B) 2.0 m/s (C) 3.0 m/s (D) 4.0 m/s (E) 6.0 m/s

17. A particle P moves around the circle of radius R

shown above under the influence of a radial force of magnitude F. What is the work done by the radial force as the particle moves from position 1 to position 2 halfway around the circle?

(A) Zero (B) RF (C) 2RF (D) πRF (E) 2πRF

Questions 18 and 19

Two blocks of wood, each of mass 2 kg, are suspended from the ceiling by strings of negligible mass, as shown above. 18. What is the tension in the upper string?

(A) 10 N (B) 20 N (C) 40 N (D) 50 N (E) 60 N

19. What is the force exerted on the upper block by the

lower string?

(A) Zero (B) 10 N upward (C) 10 N downward (D) 20 N upward (E) 20 N downward

20. The period of a mass-spring system undergoing

simple harmonic oscillation is T. If the amplitude of the mass-spring’s motion is doubled, what will be the new period? (A) ¼T (B) ½T (C) T (D) 2T (E) 4T

21. Three students were arguing about the height of a

parking garage. One student suggested that to determine the height of the garage, they simply had to drop tennis balls from the top and time the fall of the tennis balls. If the time for the ball to fall was 1.4 seconds, approximately how tall is the parking garage?

(A) 5 m (B) 7 m (C) 10 m (D) 14 m (E) 20 m

22. A deliveryman moves 10 cartons from the sidewalk,

along a 10-meter ramp to a loading dock, which is 1.5 meters above the sidewalk. If each carton has a mass of 25 kg, what is the total work done by the deliveryman on the cartons to move them to the loading dock?

(A) 2500 J (B) 3750 J (C) 10 000 J (D) 25 000 J (E) 37 500 J

23. An astronaut on the Moon simultaneously drops a

feather and a hammer. The fact that they reach the surface at the same instant shows that (A) No gravity forces act on a body in a vacuum. (B) The acceleration due to gravity on the Moon is

less than the acceleration due to gravity on the Earth.

(C) The gravitational force from the Moon on heavier objects (the hammer) is equal to the gravitational force on lighter objects (the feather).

(D) A hammer and feather have less mass on the Moon than on Earth.

(E) In the absence of air resistance all bodies at a given location fall with the same acceleration.