Excursions in Physics
PHY 3050 G
First Hour Exam

September 15, 2001

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Statistics:

High: 94

Mean: 79

Low: 34

Enter all your answers in the "scantron sheet" or the "bubble sheet". Turn in only that sheet. Anything you write on this exam will not be seen or used or considered or graded. Be sure your name is on the "bubble sheet" you hand in. Be sure your name is bubbled-in. Be sure your answers are recorded correctly.

 
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 = v_i + a t
x = x_i + v_i 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
a) by Aristotle and the ancient Greeks
b) by Ptolemy in Egypt
c) by Galileo in Italy.
This was at the time of the Renaissance, the 1600's
d) not until the beginning of the twentieth century
 
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
Galileo was a state-of-the-art experimentalist.
d) Newton invented the pendulum clock

3. 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
Galileo was also the first to use the telescope for Astronomical observations!
d) the sun dial

4. Galileo entered the University and first planned to study
a) theology
b) medicine
c) islamic studies
d) geography

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

6. Velocity is the time rate of change of
a) acceleration
b) speed
c) displacement
v = ^x / _t
d) momentum
 
7. Acceleration is the time rate of change of
a) velocity
a = ^v/_t
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 100 m in 20 s?
a) 20 m/s
b) 10 m/s
c) 5 m/s
v = ^x/_t = 100 m/20 s = 5 m/s
d) 200 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 = ^x/_t = 125 km/5 h = 25 km/h
c) 10 km/h
d) 9.8 km/h

11. Consider a train that has an acceleration of 3 m/s². Initially, at time t = 0, it has a velocity of v_i = 20 m/s. What is its speed at t = 3 s?
a) 57 m/s
b) 41 m/s
c) 29 m/s
v = v_i + a t = 20 m/s +(3 m/s²)(3 s) = 20 m/s + 9 m/s = 29 m/s
d) 9 m/s
 
12. Consider a car that starts at rest 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 = v_i + a t = 0 +(2 m/s²)(4 s) = 8 m/s
d) 4 m/s
 
13. Consider a car that starts at rest 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 = x_i + v_i t + (¹/₂) a t² = 0 + 0 + (¹/₂)(2 m/s²)(4s)² = 16 m
d) 8 m
 
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 = v_i + a t = 30 m/s+ ( - 10 m/s²)(4 s) = (30 - 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, y_i = 0.
a) 40 m
b) 20 m
c) -10 m
d) -30 m
 
16. Consider a ball that is thrown horizontally from the edge of a building with an initial velocity of 20 m/s. The building is 5 m above the driveway below. How far from the building does the ball strike the driveway?
a) 5 m
b) 10 m
c) 15 m
d) 20 m
First, how long is the ball in the air? Or, how long does it take to fall the 5 m onto the driveway below?
y = y_i + v_yi + (¹/₂) a_y t²
- 5 m = 0 + 0 + (¹/₂) ( - 10 m/s²) t²
1 s² = t²
t = 1 s
The ball is in the air for one second. How far does it move horizontally during this one second?
x = v_xi t = (20 m/s) ( 1 s ) = 20 m

17. 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
 
18. 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
 
19. 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
y = y_i + v_yi t + (¹/₂) a_y t²
0 = 0 + (20 m/s) t + (¹/₂) ( - 10 m/s²) t²
5 m/s² t² =( 20 m/s) t
5 m/s² t = 20 m/s
t = 4 s
The ball is in the air for four seconds.

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. 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
From the previous problem, we know the ball is in the air for four seconds.
x = v_xi t = (5 m/s)(4 s) = 20 m
 
21. 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
 
22. 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."
 
23. 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 = ma
d) The net force on an object is inversely proportional to the mass of the object.

24. 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
 
25. 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
 
26. 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
The net force on any object at rest is zero!
 
27. 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

28. 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 supports him with both ends. Or the rope pulls up on him twice. The total upward pull of the rope is just balanced by Harry's weight or the downward pull of gravity. So the force the rope exerts throughout the rope is 250 N, one-half Harry's weight.
d) 25 N
 
29. 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
F = m a
24 N = (8 kg) ( a ) = (8 kg)(3 m/s²)
a = 3 m/s²
c) 6 m/s²
d) 12 m/s2
 
30. A car, with mass of 1,000 kg, accelerates at 2 m/s².
a) 500 N
b) 1,000 N
c) 2,000 N
F = m a
F_net = (1,000 kg) (2 m/s²) = 2,000 N
d) 10,000 N

31. The weight of a 1,000-kg car is
a) 500 N
b) 1,000 N
c) 2,000 N
d) 10,000 N
 
32. 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
W = m g
500 N = m (10 m/s²)
m = 50 kg
F_net = W - F_friction = m a
500 N - F_friction = (50 kg) (3 m/s²) = 150 N
500 N - F_friction = 150 N
F_friction = 500 N - 150 N
F_friction = 350 N
d) 500 N
 
33. Suppose you are driving along in an open car and throw a ball straight up into the air. While the ball is still in the air you step on the brakes. Where does the ball land relative to the car?
a) behind the car
b) back into the car; We would expect it to land back in the car if the car's velocity remainded constant.
c) in front of the car
The ball will land where the car would have been if its velocity had remained constant.

34. 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.
 
35. 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.
c) made great advances in Mechanics, Gravity, Optics, and Mathematics.
d) used water clocks of his own invention to aid sailors in determining their longitude.
 
36. Galileo
a) may be called the Father of Modern Optics.
b) wrote his findings in Polish while at the University of Paduah.
c) may be called the Father of Modern Science.
Galileo was the first to put emphasis on experimental results.
d) wrote his findings about Gravity and explained calculus.
 
37. 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)
 
38. 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.

39. 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.
 

40. What value will the spring scale read in the system shown above?
a) zero
b) 25 N
c) 50 N
d) 100 N
AAAaaarrrggh! Before you can answer this question, you need to know the weight of Little Nellie Newton. So I wrote on the board to use 50 N as her weight (altho' that is an unrealistic value!)
The rope attached to the spring scale supports Nellie twice -- at her right hand and at her left hand. So the force exerted by each end of the rope is half her weight -- and that is just what is meant by the "tension" in the rope. And that is what the spring scale reads.
 
41. What is the net force on a 2-kg laboratory cart which accelerates at 3 m/s²?
a) 2 N
b) 3 N
c) 6 N
F = m a = (2 kg) ( 3 m/s²) = 6 N
d) 12 N

42. 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 = v_i + a t = (5 m/ ) + (3 m/s²)(4 s) = 5 m/s + 12 m/s = 17 m/s
c) 12 m/s
d) 8 m/s

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 far has it moved?
a) 48 m
b) 44 m
x = x_i + v_i t + (¹/₂) a t² = 0 + (5 m/s)(4 s) + (¹/₂)(3 m/s²)(4 s)² = 20 m + 24 m = 44 m
c) 32 m
d) 24 m

44. 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.

45. 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
d) 12 m/s²

a = ^v/_t = (28 m/s) / (3.5 s) = 8 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.

46. 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
F = (1,000 kg)(5 m/s²) = 5,000 N
d) 10,000 N

47. A force of 12 N is applied to a laboratory cart and an acceleration of 3 m/s² is observed. The mass of the lab cart is
a) 2 kg
b) 4 kg
F = m a
12 N = ( m ) (3 m/s²) = (4 kg)) (3 m/s²)
m = 4 kg
c) 8 kg
d) 36 kg

48. When any object moves in a circle
a) its speed must decrease
b) its acceleration continues to change direction
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. The four fundamental forces are
a) friction, weight, centripetal, inertial
b) friction, air resistance, centrifugal, weight
c) gravity, electromagnetic, strong nuclear, weak nuclear
d) gravity, electromagnetic, strong contact, weak friction

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