## Physics for Scientists And Engineers Foundations And Connections 1st Edition by Debora M. Katz – Test Bank

1. Two 0.20-kg balls, moving at 4 m/s east, strike a wall. Ball A bounces backwards at the same speed. Ball B stops. Which statement correctly describes the change in momentum of the two balls?

a.

.

b.

.

c.

.

d.

.

e.

.

*ANSWER: *

a

*POINTS: *

1

*DIFFICULTY: *

Easy

2. A car of mass *m*_{1} traveling at velocity *v* passes a car of mass *m*_{2} parked at the side of the road. The momentum of the system of two cars is

a.

0.

b.

*m*_{1}*v*.

c.

(*m*_{1} − *m*_{2})*v*.

d.

e.

(*m*_{1} + *m*_{2})*v*.

*ANSWER: *

b

*POINTS: *

1

*DIFFICULTY: *

Easy

3. A ball falls to the ground from height *h* and bounces to height *h*‘. Momentum is conserved in the ball-earth system

a.

no matter what height *h*‘ it reaches.

b.

only if *h*‘ < *h*.

c.

only if *h*‘ = *h*.

d.

only if *h*‘ > *h*.

e.

only if *h*‘ *≥** h*.

*ANSWER: *

a

*POINTS: *

1

*DIFFICULTY: *

Easy

4. The law of conservation of momentum applies to a collision between two bodies since

a.

they exert equal and opposite forces on each other.

b.

they exert forces on each other respectively proportional to their masses.

c.

they exert forces on each other respectively proportional to their velocities.

d.

they exert forces on each other respectively inversely proportional to their masses.

e.

their accelerations are proportional to their masses.

*ANSWER: *

a

*POINTS: *

1

*DIFFICULTY: *

Easy

5. The value of the momentum of a system is the same at a later time as at an earlier time if there are no

a.

collisions between particles within the system.

b.

inelastic collisions between particles within the system.

c.

changes of momentum of individual particles within the system.

d.

internal forces acting between particles within the system.

e.

external forces acting on particles of the system.

*ANSWER: *

e

*POINTS: *

1

*DIFFICULTY: *

Easy

6. A ball of mass *m** _{B}* is released from rest and acquires velocity of magnitude

*v*

*before hitting the ground. The ratio of the magnitude of the momentum the Earth acquires to the magnitude of the momentum the ball acquires is*

_{B}a.

0.

b.

.

c.

.

d.

1

e.

.

*ANSWER: *

d

*POINTS: *

1

*DIFFICULTY: *

Easy

7. A pitcher claims he can throw a baseball with as much momentum as a 3.00-g bullet moving with a speed of 1500 m/s. A baseball has a mass of 0.145 kg. What must be its speed if the pitcher’s claim is valid?

*ANSWER: *

31.0 m/s

*POINTS: *

2

*DIFFICULTY: *

Average

8. 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}

*ANSWER: *

c

*POINTS: *

2

*DIFFICULTY: *

Average

9. 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

*ANSWER: *

a

*POINTS: *

2

*DIFFICULTY: *

Average

10. 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

*ANSWER: *

d

*POINTS: *

2

*DIFFICULTY: *

Average

11. 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

*ANSWER: *

b

*POINTS: *

2

*DIFFICULTY: *

Average

12. A rocket with an initial mass of 1000 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

*ANSWER: *

a

*POINTS: *

2

*DIFFICULTY: *

Average

13. A rocket moving in outer space maintains a constant acceleration (magnitude = 20 m/s^{2}) while ejecting fuel at a speed of 15 km/s relative to the rocket. If the initial mass of the rocket is 3 000 kg, what is the magnitude of the thrust after 800 kg of fuel have been consumed?

a.

56 kN

b.

48 kN

c.

52 kN

d.

44 kN

e.

36 kN

*ANSWER: *

d

*POINTS: *

1

*DIFFICULTY: *

Easy

14. Three particles are placed in the *xy* plane. A 30-g particle is located at (3, 4) m, and a 40-g particle is located at (−2, −2) m. Where must a 20-g particle be placed so that the center of mass of the three-particle system is at the origin?

a.

(−3, −1) m

b.

(+1, +3) m

c.

(+3, −1) m

d.

(−1, −3) m

e.

(−0.5, −2) m

*ANSWER: *

e

*POINTS: *

2

*DIFFICULTY: *

Average

15. At the instant a 2.0-kg particle has a velocity of 4.0 m/s in the positive *x* direction, a 3.0-kg particle has a velocity of 5.0 m/s in the positive *y* direction. What is the speed of the center of mass of the two-particle system?

a.

3.8 m/s

b.

3.4 m/s

c.

5.0 m/s

d.

4.4 m/s

e.

4.6 m/s

*ANSWER: *

b

*POINTS: *

2

*DIFFICULTY: *

Average

16. Two bodies with masses *m*_{1} and *m*_{2} are both moving east with velocities of magnitudes *v*_{1} and *v*_{2}, where *v*_{1} is less than *v*_{2}. The magnitude of the velocity of the center of mass of this system of two bodies is

a.

less than *v*_{1}.

b.

equal to *v*_{1}.

c.

equal to the average of *v*_{1} and *v*_{2}.

d.

greater than *v*_{1} and less than *v*_{2}.

e.

greater than *v*_{2}.

*ANSWER: *

d

*POINTS: *

1

*DIFFICULTY: *

Easy

17. Assume that the average mass of each of the approximately 1 billion people in China is 55 kg. Assume that they all gather in one place and climb to the top of 2-m-high ladders. The center of mass of the Earth (*m*_{E} = 5.90 10^{24} kg) is then displaced

a.

0 m.

b.

1.84 × 10−^{23} m.

c.

1.84 × 10−^{14} m.

d.

1.80 × 10−^{13} m.

e.

2 m.

*ANSWER: *

c

*POINTS: *

2

*DIFFICULTY: *

Average

18. Two cars start at the same point, but travel in opposite directions on a circular path of radius *R*, each at speed *v*. While each car travels a distance less than , one quarter circle, the center of mass of the two cars

a.

remains at the initial point.

b.

travels along a diameter of the circle at speed *v*‘ < *v*.

c.

travels along a diameter of the circle at speed *v*‘ = *v*.

d.

travels along a diameter of the circle at speed *v*‘ > *v*.

e.

remains at the center of the circle.

*ANSWER: *

b

*POINTS: *

1

*DIFFICULTY: *

Easy

19. The linear density of a rod, in g/m, is given by . The rod extends from the origin to *x* = 0.400 m. What is the location of the center of mass of the rod?

a.

*x* = 0.213 m

b.

*x* = 0.315 m

c.

*x* = 0.384 m

d.

*x* = 0.184 m

e.

*x* = 0.208 m

*ANSWER: *

a

*POINTS: *

3

*DIFFICULTY: *

Challenging

20. A uniform thin wire has a length and is bent into a semicircular arc of radius *R*. If the wire starts at (*x*, *y*) = (*R*, 0) and curves counterclockwise to (*x*, *y*) = (−*R*, 0), what is the *y* coordinate of its center of mass?

*ANSWER: *

0.637 *R*

*POINTS: *

3

*DIFFICULTY: *

Challenging

21. 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

*ANSWER: *

a

*POINTS: *

1

*DIFFICULTY: *

Easy

22. 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}

*ANSWER: *

c

*POINTS: *

2

*DIFFICULTY: *

Average

23. 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

*ANSWER: *

a

*POINTS: *

2

*DIFFICULTY: *

Average

24. A car of mass *m*_{1} traveling at velocity *v* passes a car of mass *m*_{2} parked at the side of the road. The momentum of the system of two cars is

a.

0.

b.

*m*_{1}*v*.

c.

(*m*_{1} − *m*_{2})*v*.

d.

e.

(*m*_{1} + *m*_{2})*v*.

*ANSWER: *

b

*POINTS: *

1

*DIFFICULTY: *

Easy

25. The value of the momentum of a system is the same at a later time as at an earlier time if there are no

a.

collisions between particles within the system.

b.

inelastic collisions between particles within the system.

c.

changes of momentum of individual particles within the system.

d.

internal forces acting between particles within the system.

e.

external forces acting on particles of the system.

*ANSWER: *

e

*POINTS: *

1

*DIFFICULTY: *

Easy

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