Physics 101.002 Test 3 Answers November 15, 2007

Read each question and its set of answers very carefully. There is only one best answer for each question. Don’t be afraid to ask questions of me during the exam. Just raise your hand if you have one. Useful information: g = 32 ft/s² = 9.8 m/s².

1. What would be considered as the natural state of a rock under Aristotle's natural and violent schemes for classes of motion?

(a) rest

(b) constant velocity

(c) constant acceleration

(d) constant force

2. A ball rolling along a horizontal frictionless plane would

(a) accelerate indefinitely

(b) roll until the force used to roll it was used up

(c) roll indefinitely at a constant speed

3. Inertia is the sluggishness or apparent resistance a body offers to changes in its state of motion.

(a) True

(b) False

4. The law of inertia is Newton's law.

(a) First

(b) Second

(c) Third

(d) Gravitational

5. The inertia of a body is most closely associated with

(a) net force on body

(b) volume of the body

(c) mass of the body

(d) weight of the body

6. The kilogram is a unit of .

(a) weight

(b) volume

(c) force

(d) mass

(e) torque

7. How many Newton's does a 1 kg object weigh?

(a) 1

(b) 9.8

(c) 19.6

(d) 32

(e) 16

8. Newton's concept of motion said that the natural state of an object was

(a) constant velocity

(b) constant acceleration

(c) constant net force

9. What is the average speed of a horse that gallops a round‑trip distance of 15 km in a time of 30 min?

(a) 0

(b) 0.5 km/hr

(c) 30 km/hr

(d) 500 m/s

(e) None of the above

10. What is the average velocity for the round‑trip of the horse in question 9?

(a) 0

(b) 0.5 km/h

(c) 30 km/h

(d) 500 m/s

(e) None of the above

11. Charlie drove his car around the block at constant velocity?

(a) True

(b) False

12. A car increases its speed from 60 to 65 mi/hr in the same time that a bicycle increases its speed from rest to 5 mi/hr. The acceleration is greater for the

(a) bicycle

(b) car

(c) is the same for each

13. The speedometer of a car indicates a constant speed. Can the car be accelerating?

(a) Yes

(b) No

14. A rifle is fired straight downward from a high-altitude balloon. If the bullet leaves the barrel at 100 m/s, then its speed (in m/s) one second later (neglecting air resistance) will be about .

(a) 10

(b) 100

(c) 105

(d) 110 m/s

15. BC drops a stone down a well, looks for the splash, and determines that the well is 2 seconds "deep." How deep (in feet) is this well? (Neglect air resistance.)

(a) 32

(b) 64

(c) 16

(d) 48 ft

(e) 96 ft

16. A rock thrown straight upward rises, stops, and starts to fall again. What is its acceleration at the top of its flight?

(a) zero

(b) 32 ft/s

(c) 9.8 m/s²

(d) none of the above

17. What is the instantaneous speed of a rock in free fall after 5 seconds of a fall from rest?

(a) 160 m/s

(b) 64 ft/s

(c) 96 ft/s

(d) 32 m/s

(e) none of the above

18. Which of the following is a scalar?

(a) velocity

(b) force

(c) acceleration

(d) all of the above

(e) none of the above

19. A car moving along a straight road has a constant acceleration of 5 mi/hr/sec. What is its change in velocity after 5 sec?

(a) 5 mi/hr

(b) 20 mi/hr

(c) 1 mi/hr

(d) 25 mi/hr

(e) you need to know the cars initial velocity to answer this question

20. In the story of the wicked king and the beautiful princess that was told in class the wicked king got his way because

(a) he knew that a lever could not be used to lift more than 2.6 times the weight applied to it

(b) he made a machine that was 100% efficient

(c) he knew that a body holding itself up with a rope over a pulley would double the force on the pulley if the rope was tied to the castle

(d) wicked kings don't get their way

21. A car moving south slows to a stop. During the slowing down what is the direction of the acceleration of the car?

(a) south

(b) north

(c) down

(d) there is no acceleration

(e) acceleration does not have direction

22. The acceleration of a body is always in the direction of the net force acting on the body.

(a) True

(b) False

23. A net force of 5 Newtons is applied to a 10 kilogram mass. What is the acceleration of the mass in m/s²?

(a) 5

(b) 10

(c) 2

(d) 0.2

(e) 0.5

24. If the net force (constant in magnitude) acting on an object is always perpendicular to the velocity, then the motion is one of constant speed in a circle.

(a) True

(b) False

25. A 10 N force causes an object to have an acceleration of 5 m/s². What acceleration in m/s² will the object have if the force is doubled?

(a) 5

(b) 10

(c) 20

(d) 5/2

(e) 5/4

26. The force of friction is called when there is no relative motion between contacting media?

(a) static

(b) dynamic

(c) kinetic

(d) systematic

27. Which is true about an object that has reached terminal velocity?

(a) the acceleration of the object is 9.8 m/s²

(b) the net force on the object is zero

(c) the force of air resistance is now zero

28. A 10 lb weight is in free fall. What is the reaction force assuming the weight is the action force?

(a) the net force on the weight is 10 lb

(b) the motion will be inertial

(c) the weight exerts a force of 10 lb on the earth

29. A bug and a car collide. Which experiences the greater force?

(a) bug

(b) car

(c) neither, they both experience the same magnitude of force

30. Since action and reaction forces are exactly equal and oppositely directed, the net force on a body is always zero.

(a) True

(b) False

31. The force that the earth exerts on the moon is much greater than the force that the moon exerts on the earth.

(a) True

(b) False

32. The product of mass times velocity is most appropriately called

(a) impulse

(b) change in momentum

(c) momentum

(d) change in impulse

33. Which of the following is not a vector?

(a) impulse

(b) momentum

(c) mass

(d) All of the above

(e) None of the above

34. A force times time causes a change in momentum.

(a) True

(b) False

35. Air bags are used in cars to offer you protection during collisions by impeding your motion toward the steering wheel and windshield. Which of the following is true concerning their use?

(a) they apply the large force required to stop you

(b) they reduce the impulse necessary to stop you

(c) they increase the time for you to come to a stop

(d) all of the above

(e) none of the above

36. "Rolling with a punch" in boxing is done so that

(a) a minimum force from the punch is delivered to the body

(b) the force of the punch is delivered over a shorter period of time causing less pain

(c) the boxer can have more time to plot his next move

(d) the boxer can delay the match

(e) anger is generated faster between the opponents

37. A rubber ball and a lump of clay approach a wall with the same momentum. The clay sticks to the wall and the ball bounces off. Which delivers the most punch (impulse) to the wall?

(a) ball

(b) clay

(c) both deliver the same amount of punch

38. Why does a fired gun recoil?

(a) the bullet carries momentum in one direction, the gun must carry an equal amount in the opposite direction

(b) the gun in effect pushes on the bullet, the bullet pushes on the gun in return

(c) the gun applies an impulse to the bullet, the bullet applies an impulse to the gun in return

(d) All of the above

(e) None of the above

39. A 10,000‑kg truck traveling north at 36 m/s hits head-on a 1000‑kg car traveling south at 30 m/s. The collision is totally inelastic. What is the speed in m/s of the truck after collision?

(a) 6

(b) 36

(c) 30

(d) 17

(e) 35

40. A 5‑kg fish swimming at a speed of 1 m/s swallows an absent-minded 1‑kg fish swimming toward it at 4 m/s. The speed (in m/s) of the larger fish after lunch is

(a) 1/2

(b) 1/5

(c) 1/6

(d) 2/3

(e) 3/2