Excursions in Physics
PHY 3050 G
First Hour Exam

February 1, 2002

Statistics:

High: 100 (2!)

Mean: 82

Low: 52

For every question, also consider the following as a possible answer:
e) none of the above

Possibly useful information:
v = x / t
a = v / t
v = vi + a t
x = xi+ vi t + (1/2) a t2
v = r
F = m a
F12 = – F21
w = m g
g = 9.8 m/s2 10 m/s2

For every question, also consider the following as a possible answer:
e) none of the above

1. Kinematics is a description of motion. Motion was first well understood by Galileo in Italy at the time of the Renaissance. Dynamics is an explanation of the cause and effect of motion. Dynamics can be understood by the Laws of Motion developed by
a) Aristotle
b) Ptolemy
c) Newton
d) Joule

2. To measure the time needed to investigate motion,
a) Aristotle used a sundial.
b) Ptolemy used the pendulum clock which had just been invented.
c) Galileo invented his own water clocks.
d) Newton invented the pendulum clock.

3. Galileo took a position as a professor of mathematics and taught
a) Rubick’s cubism
b) Newton’s differential calculus
c) von Liebnetz’ integral calculus
d) Euclid’s geometry

4. Galileo was given a lifetime pension by the “city fathers” of Venice because he introduced
a) the pendulum clock.
b) the water clock.
c) the telescope.
d) the sun dial.

5. To calculate the average speed of an object, we need to know
a) force and mass.
b) distance and time.
c) distance and mass.
d) force and time.

6. Velocity is the time rate of change of
a) acceleration.
b) speed.
c) displacement.
d) momentum.

7. Acceleration is the time rate of change of
a) velocity.
b) displacement.
c) distance.
d) momentum.

8. Acceleration might be described as telling
a) where an object is located relative to an origin or reference point.
b) how fast something is moving.
c) how fast something is getting faster.
d) how long an object has been moving.

9. What is the average speed of a motorcycle that travels 150 m in 30 s?
a) 5 m/s; v = 150 m/30 s = 5 m/s
b) 10 m/s
c) 50 m/s
d) 450 m/s

10. What is the average speed of a car that travels 125 km in 5 h?
a) 625 km/h
b) 25 km/h; v = 125 km/5 h = 25 km/h
c) 10 km/h
d) 9.8 km/h

11. Consider a car that starts at rest (vi = 0) and accelerates at 2 m/s2 for 4 seconds.
At that time, t = 4 s, how fast is it going?
a) 16 m/s
b) 12 m/s
c) 8 m/s; v = vi + a t = 0 + (2 m/s2)(4 s) = 0 + 8 m/s = 8 m/s
d) 4 m/s

12. Consider a car that starts at rest (vi = 0) and accelerates at 2 m/s2 for 4 seconds.
At that time, t = 4 s, how far has it gone?
a) 32 m
b) 24 m
c) 16 m; x = xi + vi t + (1/2) a t2 = 0 + 0 + (1/2)(2 m/s2)(4 s)2 = 16 m
d) 8 m

13. Consider a train that has an acceleration of 3 m/s2. Initially, at time t = 0, it has a velocity of v= 20 m/s. What is its speed at t = 3 s?
a) 57 m/s
b) 41 m/s
c) 29 m/s; v = vi + a t = 20 m/s + (3 m/s2)(3 s) = 20 m/s + 9 m/s = 29 m/s
d) 9 m/s

14. Consider a ball that is thrown upward at the edge of a canyon with an initial velocity of 30 m/s. Four seconds later, what is its velocity?
a) 40 m/s
b) 20 m/s
c) - 10 m/s; v = vi + a t = 30 m/s + ( - 10 m/s2)(4 s) = 30 m/s - 40 m/s = - 10 m/s
d) - 30 m/s

15. Consider a ball that is thrown straight upward at the edge of a canyon with an initial velocity of 30 m/s. Four seconds later, where is it located? Take its initial position, at the edge of the canyon, to be the origin; that is, yi = 0.
a) 40 m; y = yi + vyi t + (1/2) ay t2 = 0 + (30 m/s)(4 s) + (1/2)( - 10 m/s2)(4 s)2
y = 0 + 120 m - 80 m = 40 m

b) 20 m
c) 110 m
d) 130 m

16. Consider a ball thrown horizontally from the edge of a building with an initial velocity of 20 m/s. The ball is thrown from 5 m above the ground. How long is it in the air? That is, when does it strike the ground?
a) 0.5 s
b) 1.0 s; y = yi + vyi t + (1/2) ay t2 = 0 + 0 + (1/2)( - 10 m/s2)(t)2
y = - 5 m = 0 + 0 + (1/2)( - 10 m/s2)(t)2 = - 5 m/s2 (t2)
1 s2 = t2

1 s = t
c) 1.5 s
d) 2.0 s

17. Consider a ball that is thrown horizontally from the edge of a building with an initial velocity of 20 m/s. The ball is thrown from 5 m above the ground. How far from the building does the ball strike the ground?
a) 5 m
b) 10 m
c) 15 m
d) 20 m; x = vx t = (20 m/s)(1 s) = 20 m

18. When a ball or stone or other object is thrown or hit or fired, and air resistance can be neglected, the resulting motion is known as projectile motion. The path of an object in projectile motion is
a) a quadrant of a circle
b) a hyperbola
c) a parabola
d) a straight line

19. Projectile motion is a combination of
a) horizontal motion with constant, non-zero acceleration and vertical motion with constant velocity
b) horizontal motion with constant non-zero acceleration and vertical motion with constant, non-zero acceleration
c) horizontal motion with constant velocity and vertical motion with constant, non-zero acceleration
d) horizontal motion with constant velocity and vertical motion with constant velocity

20. Consider a ball thrown from a level surface with an initial upward velocity of 20 m/s and an initial horizontal velocity of 5 m/s. How long is the ball in the air?
a) 0.5 s
b) 1.0 s
c) 2.0 s
d) 4.0 s; v = vi + a t
- 40 m/s = ( - 10 m/s2) t
4 s = t
t = 4 s

[[ The key was correct ]]

21. Consider a ball thrown from a level surface with an initial upward velocity of 20 m/s and an initial horizontal velocity of 5 m/s. Where does it land? That is, measured from its initial position, where does it come back to and strike the level surface?
a) 5 m
b) 10 m
c) 15 m
d) 20 m; x = xi + v t = 0 + (5 m/s)(4 s) = 20 m

[[ The key was correct ]]

22. A golf ball is given a velocity of 8 m/s horizontally and 15 m/s vertically. How long is it in the air, before coming back to its initial vertical height? That is, how long is it in the air before striking the level ground?
a) 1.5 s
b) 2.0 s
c) 3.0 s; v = vi + a t
v = - 15 m/s = 15 m/s + ( - 10 m/s2) t

- 30 m/s = ( - 10 m/s2) t
t = 3 s

d) 4.0 s

23. A golf ball is given a velocity of 8 m/s horizontally and 15 m/s vertically. How far, horizontally, does it travel before coming back to its initial vertical height? That is, how far does it travel before hitting the level ground?
a) 8 m
b) 12 m
c) 24 m; x = vx t = (8 m/s) (3 s) = 24 m
d) 48 m

24. If a Ferris wheel has a diameter of 10 m (that means r = 5 m) and requires 20 seconds to make a revolution, what is the linear speed of a passenger? C = 2 r; = 3.14
a) 0.8 m/s
b) 1.6 m/s; v = dist/time = C/t = 2 r / t = 2 (5 m) / 20 s = (/2) m/s = 1.6 m/s
c) 3.1 m/s
d) 6.3 m/s

25. Newton's First Law of Motion states that, in the absence of a net force, an object in motion will
a) eventually come to rest
b) continue in motion but slow down until it stops
c) continue in motion with the same speed along the same straight line
d) continue along the same straight line with a decrease in speed

26. Newton's Second Law of Motion explains the cause of motion and may be stated as
a) "All motion is relative."
b) "All objects fall with the same velocity."
c) "The acceleration of an object is proportional to the net force on the object and inversley proportional to the object's mass." a = F / m
d) "The acceleration of an object is proportional to the product of the object's mass and the net force on it."

27. Newton's Second Law of Motion explains the cause of motion and may be stated as
a) The net force on an object is inversely proportional to its weight.
b) The net force on an object produces an acceleration that is proportional to the time of action of that force.
c) The net force on an object is equal to the product of the mass of that object and its acceleration. F = m a
d) The net force on an object is inversely proportional to the mass of the object.

28. Newton’s Third Law of Motion explains how two objects interact and may be stated as
a) "All motion is relative."
b) "All objects fall with the same velocity."
c) "You cannot touch without being touched."
d) "The acceleration of an object is proportional to the product of the object's mass and the net force on it."

29. Mass is a measure of
a) the volume of an object
b) the size of an object
c) how difficult it is to change the motion of an object
d) the velocity of an object

30. The weight of an object is
a) the same thing as the mass of an object
b) the sum of all the forces on an object
c) the force of gravity on an object
d) always less than the mass, even in a vacuum

31. The net force on a 1-kg object, at rest, is
a) 9.8 N
b) 4.9 N
c) 1.00 N
d) zero

32. The net force on a 1-kg object, in free fall, is
a) 9.8 N
b) 4.9 N
c) 1.00 N
d) zero

33. Harry the Painter has a weight of 500 N. When he is suspended as shown in the sketch here, what is the tension in the rope?
a) 1000 N
b) 500 N
c) 250 N; The rope pulls UP on Harry TWICE.
d) 25 N

34. What will the spring scale read in the arrangement shown here?
a) zero
b) 50 N
c) 100 N
d) 200 N

35. A force of 24 N acts on an object whose mass is 8 kg.
This causes the object to accelerate at
a) 2 m/s2
b) 3 m/s2
c) 6 m/s2
d) 12 m/s2

36. What is the mass of a fireman whose weight is 500 N?
a) 5000 kg
b) 500 kg
c) 50 kg
d) 5 kg

37. A fireman, whose weight is 500 N, slides down a pole with an acceleration of 3 m/s2. The forces that act on him are his weight pulling him down and the force of friction pulling up on him to slow him down. The force of friction must be
a) 90 N
b) 150 N
c) 350 N; F = Fnet = m a = (50 kg)(3 m/s2) = 150 N
Fnet = W - Ffrict = 500 N - Ffrict = 150 N
Ffrict = 350 N

d) 500 N

38. If a sailor drops a wrench from the top of a tall mast on a moving ship, it will fall and hit the deck
a) in front of the base of the.
b) at the base of the mast.
c) behind the base of the mast.

39. Sir Isaac Newton
a) first discovered the Law of Falling Bodies while at the University of Pisa.
b) was a close friend of Liebnitz and encouraged his early development of calculus.
d) used water clocks of his own invention to aid sailors in determining their longitude.

40. The hallmark of Modern Science is that
a) theories are accepted or rejected based upon the background or reputation of the scientists who propose them (horrors!)
b) predictions of theories must be tested by and agree with experimental results.
c) theories must have elegant mathematical equations.
d) predictions of theories must not contradict established authorities (such as Plato or Pythagores)

41. When applying Newton's Second Law of Motion, F = ma,
a) F is always the largest force present.
b) F is always the net force -- or the sum of all the forces present.
c) m is always the largest mass in the system.
d) m must be the smallest mass in the system.

42. Consider a 2-kg laboratory cart which accelerates at 3 m/s2. What is the net force on the cart?
a) 2 N
b) 3 N
c) 6 N; F = m a = (2 kg)(3 m/s2) = 6 N
d) 12 N

43. Consider a 2-kg lab cart which has an initial velocity of 5 m/s and then accelerates at 3 m/s2 for four seconds. At that time, t = 4 s, how fast is it moving?
a) 20 m/s
b) 17 m/s; v = vi + a t = 5 m/s + (3 m/s2)(4 s) = (5 + 12) m/s = 17 m/s
c) 12 m/s
d) 8 m/s

44. Consider a 2-kg lab cart which has an initial velocity of 5 m/s and then accelerates at 3 m/s2 for four seconds. At that time, t = 4 s, how far has it moved?
a) 48 m
b) 44 m; x = xi + vi t + (1/2) a t2 = 0 + (5 m/s)(4 s) + (1/2)(3 m/s2)(4 s)2
x = (0 + 20 + 24) m = 44 m

c) 32 m
d) 24 m

45. In the absence of air resistance,
a) heavier objects fall with a greater acceleration than lighter objects.
b) heavier objects fall with the same acceleration as lighter objects.
c) heavier objects fall with a smaller acceleration than lighter objects.

46. A roller coaster is launched from rest to 28 m/s (that’s about 100 km/h or 60 mi/h) in 3.5 seconds. That is an acceleration of
a) 2 m/s2
b) 4 m/s2
c) 8 m/s2; a = v/t = (28 m/s)/(3.5 s) = 8 m/s2
d) 12 m/s2

The Rock 'n' Roller Coaster at the Disney-MGM Studios inWalt Disney World launches from rest to 60 mi/h in 2.8 seconds for an acceleration of about 9.6 m/s2.

47. A particular roller coaster is launched with an acceleration of 5 m/s2. What is the net force required to launch a 1,000-kg car?
a) 200 N
b) 1,000 N
c) 5,000 N; F = m a = (1 000 kg)(5 m/s2) = 5 000 N
d) 10,000 N

48. When any object moves in a circle
a) its speed must decrease
b) its acceleration continues to change direction; its acceleration always points toward the center
c) its velocity is directed toward the center of the circle
d) its acceleration is tangent to the circle

49. The net force on any object which moves in a circle
a) causes the speed to increase.
b) is directed along a line tangent to the circle.
c) increases as the object slows down.
d) points toward the center of the circle.

50. When using Newton's Third Law of Motion, F12 = - F21, the two forces
a) always cancel so this applies only to systems in equilibrium.
b) always act on different objects.
c) must act on the same object.
d) are always perpendicular to each other.