## PHYSICS FOR SCIENTISTS AND ENGINEERS 9TH EDITION BY SERWAY – TEST BANK

**Chapter 9—Linear Momentum and Collisions**

**MULTIPLE CHOICE**

- A 2 000-kg truck traveling at a speed of 6.0 m/s makes a 90° turn in a time of 4.0 s and emerges from this turn with a speed of 4.0 m/s. What is the magnitude of the average resultant force on the truck during this turn?

a.

4.0 kN

b.

5.0 kN

c.

3.6 kN

d.

6.4 kN

e.

0.67 kN

ANS: C PTS: 2 DIF: Average

- A 1.2-kg object moving with a speed of 8.0 m/s collides perpendicularly with a wall and emerges with a speed of 6.0 m/s in the opposite direction. If the object is in contact with the wall for 2.0 ms, what is the magnitude of the average force on the object by the wall?

a.

9.8 kN

b.

8.4 kN

c.

7.7 kN

d.

9.1 kN

e.

1.2 kN

ANS: B PTS: 2 DIF: Average

- A 1.5-kg playground ball is moving with a velocity of 3.0 m/s directed 30° below the horizontal just before it strikes a horizontal surface. The ball leaves this surface 0.50 s later with a velocity of 2.0 m/s directed 60° above the horizontal. What is the magnitude of the average resultant force on the ball?

a.

14 N

b.

11 N

c.

18 N

d.

22 N

e.

3.0 N

ANS: B PTS: 2 DIF: Average

- The only force acting on a 2.0-kg object moving along the
*x*axis is shown. If the velocity*v*is -2.0 m/s at_{x}*t*= 0, what is the velocity at*t*= 4.0 s?

a.

-2.0 m/s

b.

-4.0 m/s

c.

-3.0 m/s

d.

+1.0 m/s

e.

+5.0 m/s

ANS: C PTS: 2 DIF: Average

- The only force acting on a 2.0-kg object moving along the
*x*axis is shown. If the velocity*v*is +2.0 m/s at_{x}*t*= 0, what is the velocity at*t*= 4.0 s?

a.

+4.0 m/s

b.

+5.0 m/s

c.

+6.0 m/s

d.

+7.0 m/s

e.

+2.0 m/s

ANS: A PTS: 2 DIF: Average

- The speed of a 2.0-kg object changes from 30 m/s to 40 m/s during a 5.0-s time interval. During this same time interval, the velocity of the object changes its direction by 90°. What is the magnitude of the average total force acting on the object during this time interval?

a.

30 N

b.

20 N

c.

40 N

d.

50 N

e.

6.0 N

ANS: B PTS: 2 DIF: Average

- A 3.0-kg ball with an initial velocity of (4+ 3) m/s collides with a wall and rebounds with a velocity of (-4 + 3) m/s. What is the impulse exerted on the ball by the wall?

a.

+24Ns

b.

-24 Ns

c.

+18 Ns

d.

-18 Ns

e.

+8.0 Ns

ANS: B PTS: 2 DIF: Average

- A 2.4-kg ball falling vertically hits the floor with a speed of 2.5 m/s and rebounds with a speed of 1.5 m/s. What is the magnitude of the impulse exerted on the ball by the floor?

a.

9.6 Ns

b.

2.4 Ns

c.

6.4 Ns

d.

1.6 Ns

e.

1.0 Ns

ANS: A PTS: 2 DIF: Average

- An 8.0-kg object moving 4.0 m/s in the positive
*x*direction has a one-dimensional collision with a 2.0-kg object moving 3.0 m/s in the opposite direction. The final velocity of the 8.0-kg object is 2.0 m/s in the positive*x*direction. What is the total kinetic energy of the two-mass system after the collision?

a.

32 J

b.

52 J

c.

41 J

d.

25 J

e.

29 J

ANS: C PTS: 3 DIF: Challenging

- A 1.6-kg ball is attached to the end of a 0.40-m string to form a pendulum. This pendulum is released from rest with the string horizontal. At the lowest point of its swing, when it is moving horizontally, the ball collides with a 0.80-kg block initially at rest on a horizontal frictionless surface. The speed of the block just after the collision is 3.0 m/s. What is the speed of the ball just after the collision?

a.

1.7 m/s

b.

1.1 m/s

c.

1.5 m/s

d.

1.3 m/s

e.

2.1 m/s

ANS: D PTS: 3 DIF: Challenging

- A 4.0-kg particle is moving horizontally with a speed of 5.0 m/s when it strikes a vertical wall. The particle rebounds with a speed of 3.0 m/s. What is the magnitude of the impulse delivered to the particle?

a.

24 N×s

b.

32 N×s

c.

40 N×s

d.

30 N×s

e.

8.0 N×s

ANS: B PTS: 2 DIF: Average

- A 2.0-kg object moving with a velocity of 5.0 m/s in the positive
*x*direction strikes and sticks to a 3.0-kg object moving with a speed of 2.0 m/s in the same direction. How much kinetic energy is lost in this collision?

a.

2.4 J

b.

9.6 J

c.

5.4 J

d.

0.6 J

e.

6.0 J

ANS: C PTS: 3 DIF: Challenging

- A 10-g bullet moving 1 000 m/s strikes and passes through a 2.0-kg block initially at rest, as shown. The bullet emerges from the block with a speed of 400 m/s. To what maximum height will the block rise above its initial position?

a.

78 cm

b.

66 cm

c.

56 cm

d.

46 cm

e.

37 cm

ANS: D PTS: 2 DIF: Average

- A 12-g bullet moving horizontally strikes and remains in a 3.0-kg block initially at rest on the edge of a table. The block, which is initially 80 cm above the floor, strikes the floor a horizontal distance of 120 cm from its initial position. What was the initial speed of the bullet?

a.

0.68 km/s

b.

0.75 km/s

c.

0.81 km/s

d.

0.87 km/s

e.

0.41 km/s

ANS: B PTS: 3 DIF: Challenging

- A 6.0-kg object moving 5.0 m/s collides with and sticks to a 2.0-kg object. After the collision the composite object is moving 2.0 m/s in a direction opposite to the initial direction of motion of the 6.0-kg object. Determine the speed of the 2.0-kg object before the collision.

a.

15 m/s

b.

7.0 m/s

c.

8.0 m/s

d.

23 m/s

e.

11 m/s

ANS: D PTS: 2 DIF: Average

- A 2.0-kg object moving 5.0 m/s collides with and sticks to an 8.0-kg object initially at rest. Determine the kinetic energy lost by the system as a result of this collision.

a.

20 J

b.

15 J

c.

30 J

d.

25 J

e.

5.0 J

ANS: A PTS: 2 DIF: Average

- A 1.6-kg block is attached to the end of a 2.0-m string to form a pendulum. The pendulum is released from rest when the string is horizontal. At the lowest point of its swing when it is moving horizontally, the block is hit by a 10-g bullet moving horizontally in the opposite direction. The bullet remains in the block and causes the block to come to rest at the low point of its swing. What was the magnitude of the bullet’s velocity just before hitting the block?

a.

1.0 km/s

b.

1.6 km/s

c.

1.2 km/s

d.

1.4 km/s

e.

1.8 km/s

ANS: A PTS: 2 DIF: Average

- A 3.0-kg mass sliding on a frictionless surface has a velocity of 5.0 m/s east when it undergoes a one-dimensional inelastic collision with a 2.0-kg mass that has an initial velocity of 2.0 m/s west. After the collision the 3.0-kg mass has a velocity of 1.0 m/s east. How much kinetic energy does the two-mass system lose during the collision?

a.

22 J

b.

24 J

c.

26 J

d.

20 J

e.

28 J

ANS: B PTS: 3 DIF: Challenging

- A 3.0-kg mass is released from rest at point A of a circular frictionless track of radius 0.40 m as shown in the figure. The mass slides down the track and collides with a 1.4-kg mass that is initially at rest on a horizontal frictionless surface. If the masses stick together, what is their speed after the collision?

a.

2.1 m/s

b.

1.7 m/s

c.

1.9 m/s

d.

1.5 m/s

e.

2.3 m/s

ANS: C PTS: 2 DIF: Average

- A 3.0-kg mass is sliding on a horizontal frictionless surface with a speed of 3.0 m/s when it collides with a 1.0-kg mass initially at rest as shown in the figure. The masses stick together and slide up a frictionless circular track of radius 0.40 m. To what maximum height,
*h*, above the horizontal surface will the masses slide?

a.

0.18 m

b.

0.15 m

c.

0.21 m

d.

0.26 m

e.

0.40 m

ANS: D PTS: 2 DIF: Average

- A 10-g bullet moving horizontally with a speed of 2.0 km/s strikes and passes through a 4.0-kg block moving with a speed of 4.2 m/s in the opposite direction on a horizontal frictionless surface. If the block is brought to rest by the collision, what is the kinetic energy of the bullet as it emerges from the block?

a.

0.51 kJ

b.

0.29 kJ

c.

0.80 kJ

d.

0.13 kJ

e.

20 kJ

ANS: A PTS: 3 DIF: Challenging

- A 10-g bullet moving horizontally with a speed of 1.8 km/s strikes and passes through a 5.0-kg block initially at rest on a horizontal frictionless surface. The bullet emerges from the block with a speed of 1.0 km/s. What is the kinetic energy of the block immediately after the bullet emerges?

a.

8.0 J

b.

6.4 J

c.

5.3 J

d.

9.4 J

e.

10 J

ANS: B PTS: 2 DIF: Average

- A pendulum consists of a 2.0-kg block hanging on a 1.5-m length string. A 10-g bullet moving with a horizontal velocity of 900 m/s strikes, passes through, and emerges from the block (initially at rest) with a horizontal velocity of 300 m/s. To what maximum height above its initial position will the block swing?

a.

32 cm

b.

38 cm

c.

46 cm

d.

27 cm

e.

9 cm

ANS: C PTS: 2 DIF: Average

- A 1.0-kg ball is attached to the end of a 2.5-m string to form a pendulum. This pendulum is released from rest with the string horizontal. At the lowest point in its swing when it is moving horizontally, the ball collides elastically with a 2.0-kg block initially at rest on a horizontal frictionless surface. What is the speed of the block just after the collision?

a.

2.3 m/s

b.

4.7 m/s

c.

3.5 m/s

d.

3.0 m/s

e.

7.0 m/s

ANS: B PTS: 3 DIF: Challenging

- A 3.0-kg object moving in the positive
*x*direction has a one-dimensional elastic collision with a 5.0-kg object initially at rest. After the collision the 5.0-kg object has a velocity of 6.0 m/s in the positive*x*direction. What was the initial speed of the 3.0 kg object?

a.

6.0 m/s

b.

7.0 m/s

c.

4.5 m/s

d.

8.0 m/s

e.

5.5 m/s

ANS: D PTS: 2 DIF: Average

- A 3.0-kg object moving 8.0 m/s in the positive
*x*direction has a one-dimensional elastic collision with an object (mass =*M*) initially at rest. After the collision the object of unknown mass has a velocity of 6.0 m/s in the positive*x*direction. What is*M*?

a.

7.5 kg

b.

5.0 kg

c.

6.0 kg

d.

4.2 kg

e.

8.0 kg

ANS: B PTS: 2 DIF: Average

- A 6.0-kg object moving 2.0 m/s in the positive
*x*direction has a one-dimensional elastic collision with a 4.0-kg object moving 3.0 m/s in the opposite direction. What is the total kinetic energy of the two-mass system after the collision?

a.

30 J

b.

62 J

c.

20 J

d.

44 J

e.

24 J

ANS: A PTS: 1 DIF: Easy

- Two blocks with masses 2.0 kg and 3.0 kg are placed on a horizontal frictionless surface. A light spring is placed in a horizontal position between the blocks. The blocks are pushed together, compressing the spring, and then released from rest. After contact with the spring ends, the 3.0-kg mass has a speed of 2.0 m/s. How much potential energy was stored in the spring when the blocks were released?

a.

15 J

b.

3.0 J

c.

6.0 J

d.

12 J

e.

9.0 J

ANS: A PTS: 2 DIF: Average

- An 80-g particle moving with an initial speed of 50 m/s in the positive
*x*direction strikes and sticks to a 60-g particle moving 50 m/s in the positive*y*direction. How much kinetic energy is lost in this collision?

a.

96 J

b.

89 J

c.

175 J

d.

86 J

e.

110 J

ANS: D PTS: 3 DIF: Challenging

- A 2.0-kg object moving 3.0 m/s strikes a 1.0-kg object initially at rest. Immediately after the collision, the 2.0-kg object has a velocity of 1.5 m/s directed 30° from its initial direction of motion. What is the
*x*component of the velocity of the 1.0-kg object just after the collision?

a.

3.7 m/s

b.

3.4 m/s

c.

1.5 m/s

d.

2.4 m/s

e.

4.1 m/s

ANS: B PTS: 2 DIF: Average

- A 2.0-kg object moving 3.0 m/s strikes a 1.0-kg object initially at rest. Immediately after the collision, the 2.0-kg object has a velocity of 1.5 m/s directed 30° from its initial direction of motion. What is the
*y*component of the velocity of the 1.0-kg object just after the collision?

a.

-3.7 m/s

b.

-3.4 m/s

c.

-1.5 m/s

d.

-2.4 m/s

e.

-4.1 m/s

ANS: C PTS: 2 DIF: Average

- A 6.0-kg object, initially at rest in free space, “explodes” into three segments of equal mass. Two of these segments are observed to be moving with equal speeds of 20 m/s with an angle of 60° between their directions of motion. How much kinetic energy is released in this explosion?

a.

2.4 kJ

b.

2.9 kJ

c.

2.0 kJ

d.

3.4 kJ

e.

1.2 kJ

ANS: C PTS: 3 DIF: Challenging

- A 5.0-g particle moving 60 m/s collides with a 2.0-g particle initially at rest. After the collision each of the particles has a velocity that is directed 30° from the original direction of motion of the 5.0-g particle. What is the speed of the 2.0-g particle after the collision?

a.

72 m/s

b.

87 m/s

c.

79 m/s

d.

94 m/s

e.

67 m/s

ANS: B PTS: 3 DIF: Challenging

- A 1.0-kg object moving 9.0 m/s collides with a 2.0-kg object moving 6.0 m/s in a direction that is perpendicular to the initial direction of motion of the 1.0-kg object. The two masses remain together after the collision, and this composite object then collides with and sticks to a 3.0-kg object. After these collisions, the final composite (6.0-kg) object remains at rest. What was the speed of the 3.0-kg object before the collisions?

a.

15 m/s

b.

10 m/s

c.

5.0 m/s

d.

20 m/s

e.

25 m/s

ANS: C PTS: 2 DIF: Average

- A 3.0-kg mass sliding on a frictionless surface explodes into three 1.0-kg masses. After the explosion the velocities of the three masses are: (1) 9.0 m/s, north; (2) 4.0 m/s, 30° south of west; and (3) 4.0 m/s, 30° south of east. What was the magnitude of the original velocity of the 3.0-kg mass?

a.

1.7 m/s

b.

1.0 m/s

c.

1.3 m/s

d.

2.0 m/s

e.

2.8 m/s

ANS: A PTS: 2 DIF: Average

- A 3.0-kg mass moving in the positive
*x*direction with a speed of 10 m/s collides with a 6.0-kg mass initially at rest. After the collision, the speed of the 3.0-kg mass is 8.0 m/s, and its velocity vector makes an angle of 35° with the positive*x*axis. What is the magnitude of the velocity of the 6.0-kg mass after the collision?

a.

2.2 m/s

b.

2.9 m/s

c.

4.2 m/s

d.

3.5 m/s

e.

4.7 m/s

ANS: B PTS: 3 DIF: Challenging

- A 5.0-kg mass with an initial velocity of 4.0 m/s, east collides with a 4.0-kg mass with an initial velocity of 3.0 m/s, west. After the collision the 5.0-kg mass has a velocity of 1.2 m/s, south. What is the magnitude of the velocity of the 4.0-kg mass after the collision?

a.

2.0 m/s

b.

1.5 m/s

c.

1.0 m/s

d.

2.5 m/s

e.

3.0 m/s

ANS: D PTS: 2 DIF: Average

- A 4.0-kg mass has a velocity of 4.0 m/s, east when it explodes into two 2.0-kg masses. After the explosion one of the masses has a velocity of 3.0 m/s at an angle of 60° north of east. What is the magnitude of the velocity of the other mass after the explosion?

a.

7.9 m/s

b.

8.9 m/s

c.

7.0 m/s

d.

6.1 m/s

e.

6.7 m/s

ANS: C PTS: 2 DIF: Average

- A 4.2-kg object, initially at rest, “explodes” into three objects of equal mass. Two of these are determined to have velocities of equal magnitudes (5.0 m/s) with directions that differ by 90°. How much kinetic energy was released in the explosion?

a.

70 J

b.

53 J

c.

60 J

d.

64 J

e.

35 J

ANS: A PTS: 2 DIF: Average

- A 4.0-kg mass, initially at rest on a horizontal frictionless surface, is struck by a 2.0-kg mass moving along the
*x*axis with a speed of 8.0 m/s. After the collision, the 2.0-kg mass has a speed of 4.0 m/s at an angle of 37° from the positive*x*axis. What is the speed of the 4.0-kg mass after the collision?

a.

2.0 m/s

b.

2.7 m/s

c.

4.9 m/s

d.

2.4 m/s

e.

3.6 m/s

ANS: B PTS: 2 DIF: Average

- At an instant when a particle of mass 50 g has an acceleration of 80 m/s
^{2}in the positive*x*direction, a 75-g particle has an acceleration of 40 m/s^{2}in the positive*y*direction. What is the magnitude of the acceleration of the center of mass of this two-particle system at this instant?

a.

60 m/s^{2}

b.

56 m/s^{2}

c.

40 m/s^{2}

d.

50 m/s^{2}

e.

46 m/s^{2}

ANS: C PTS: 2 DIF: Average

- At an instant when a particle of mass 80 g has a velocity of 25 m/s in the positive
*y*direction, a 75-g particle has a velocity of 20 m/s in the positive*x*direction. What is the speed of the center of mass of this two-particle system at this instant?

a.

16 m/s

b.

45 m/s

c.

23 m/s

d.

20 m/s

e.

36 m/s

ANS: A PTS: 2 DIF: Average

- Three particles are placed in the
*xy*plane. A 40-g particle is located at (3, 4) m, and a 50-g particle is positioned at (-2, -6) m. Where must a 20-g particle be placed so that the center of mass of this three-particle system is located at the origin?

a.

(-1, -3) m

b.

(-1, 2) m

c.

(-1, 12) m

d.

(-1, 7) m

e.

(-1, 3) m

ANS: D PTS: 2 DIF: Average

- A rocket engine consumes 450 kg of fuel per minute. If the exhaust speed of the ejected fuel is 5.2 km/s, what is the thrust of the rocket?

a.

42 kN

b.

39 kN

c.

45 kN

d.

48 kN

e.

35 kN

ANS: B PTS: 2 DIF: Average

- A rocket with an initial mass of 1 000 kg adjusts its thrust by varying the rate at which mass is ejected. The ejection speed relative to the rocket is 40 km/s. If the acceleration of the rocket is to have a magnitude of 20 m/s
^{2}at an instant when its mass is 80% of the original mass, at what rate is mass being ejected at that instant? Ignore any external forces on the rocket.

a.

0.40 kg/s

b.

0.50 kg/s

c.

0.60 kg/s

d.

0.70 kg/s

e.

0.80 kg/s

ANS: A PTS: 2 DIF: Average

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