Excursions in Physics
PHY 3050C
First Hour Exam
September 15, 2000

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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 and SSN are on the "bubble sheet" you hand in. Be sure your name and SSN are 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 = vi + a t
x = xi + vi t + (1/2) a t2

F = m a
F12 = - F21
w = mg
g = 9.8 m/s2 10 m/s2

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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 Mozart during the Orchestral Epoch.
b) by Aristotle and the ancient Greeks during the Golden Age.
c) by Ptolemy in Egypt during the Ramses Dynasty.
d) by Galileo in Italy during the Renaissance.


2. 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 astrolabe.


3. Galileo took a position as a professor of mathematics and taught

a) Euclid’s geometry.
b) Newton’s differential calculus. Newton was born the year Galileo died.
c) von Liebnitz’ integral calculus. von Liebnitz was a contemporary of Newton's.
d) Rubick’s cubism. Rubick lived in the twentieth century (and is probably still alive).


4. Velocity is the time rate of change of

a) acceleration.
b) speed.
c) displacement.
d) momentum.

 
5. Acceleration is the time rate of change of

a) velocity.
b) displacement.
c) distance.
d) momentum.

 
6. 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.


7. What is the average speed of a car that travels 250 km in 5 h?

a) 1250 km/h
b) 625 km/h
c) 50 km/h; = 250 km/5 h = 50 km/h
d) 25 km/h

 
8. Consider a train that has an acceleration of 3 m/s2. Initially, at time t = 0, it has a velocity of vi = 30 m/s. What is its speed at t = 4 s?

a) 64 m/s
b) 44 m/s
c) 29 m/s
d) 12 m/s

e) none of the above; v = vi + a t = ( 30 m/s ) + ( 3 m/s2 )( 4 s ) = (30 + 12) m/s = 42 m/s


9. Consider a car that starts at rest ( vi = 0 ) and accelerates at 3 m/s2 for 4 seconds. At that time, t = 4 s, how fast is it going?

a) 18 m/s
b) 12 m/s; v = vi + a t = ( 0 ) + ( 3 m/s2 )( 4 s ) = 12 m/s

c) 9 m/s
d) 6 m/s

10. Consider a car that starts at rest ( vi = 0 ) a and accelerates at 3 m/s2 for 4 seconds.

At that time, t = 4 s, how far has it gone?

a) 48 m
b) 24 m;
x = xi + vi t + (1/2) a t2

x = 0 + 0 + (1/2) ( 3 m/s2 )( 4 s ) 2

x = (1/2) ( 3 m/s2 )( 16 s 2 )

x = 24 m

c) 12 m
d) 6 m

 

11. Consider a ball that is thrown upward at the edge of a canyon with an initial velocity of 20 m/s. Three seconds later, what is its velocity?

a) 30 m/s
b) 15 m/s
c) - 10 m/s;
v = vi + a t = ( 20 m/s ) + ( - 10 m/s2 )( 3 s ) = (20 - 30) m/s = - 10 m/s

d) - 30 m/s


12. Consider a ball that is thrown straight upward at the edge of a canyon with an initial velocity of 20 m/s. Three 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) 30 m
b) 15 m;
x = xi + vi t + (1/2) a t2

y = yi + vyi t + (1/2) ay t2

y = yi + vyi t + (1/2) ( - g ) t2

y = 0+ ( 20 m/s ) ( 3 s) + (1/2) ( - 10 m/s2 ) ( 3 s )2

y = 0+ 60 m - (1/2) ( 10 m/s2 ) ( 9 s2 )

y = 0+ 60 m - 45 m

y = 15 m

c) - 10 m
d) - 30 m

13. A rock climber dislodges a rock and notices that it falls for 5 seconds before hitting the canyon floor below. How fast is it going when it strikes the canyon floor?

a) 10 m/s
b) 15 m/s
c) 25 m/s
d) 50 m/s;
v = vi + a t

v = 0 + ( - 10 m/s2 ) ( 5 s )

v = - 50 m/s (for the velocity with the minus sign meaning "down")

v = 50 m/s (for the "speed" or simply "how fast")


14. A rock climber dislodges a rock and notices that it falls for 5 seconds before hitting the canyon floor below. How far has it fallen when it strikes the canyon floor?

a) 10 m
b) 60 m
c) 125 m
x = xi + vi t + (1/2) a t2

y = yi + vyi t + (1/2) ay t2

y = yi + vyi t + (1/2) ( - g ) t2

y = 0+ 0 + (1/2) ( - 10 m/s2 ) ( 5 s )2

y = 0+ 0 + (1/2) ( - 10 m/s2 ) ( 25 s2 )

y = 125 m

d) 250 m

 
15. 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 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, we must ask "how long is it in the air?"
y = (1/2) ay t2

y = (1/2) ( - g ) t2

When it hits the driveway, its vertical position is y = - 5 m, 5 m below where it started.

- 5 m = (1/2) ( - 10 m/s2 ) t2

1 s2 = t2

1 s = t

Now, how far horizontally does it travel in this time?

x = v t

x = ( 20 m/s ) ( 1 s )

x = 20 m


16. 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

 
17. 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) 1.0 s
b) 2.0 s
c) 4.0 s
First, we must ask "how long is it in the air?"
y = y + vyi + (1/2) ay t2 is somewhat difficult to solve. An easier approach is to use

vy = vyi + ay t

When it gets back to the level surface, vy = - vyi

- 20 m/s = 20 m/s + ( - 10 m/s2 ) t

- 40 m/s = ( - 10 m/s2 ) t

4 s = t

d) 8.0 s

 

y = (1/2) ( - g ) t2

- 5 m = (1/2) ( - 10 m/s2 ) t2

1 s2 = t2

1 s = t

Now, how far horizontally does it travel in this time?

x = v t

x = ( 20 m/s ) ( 1 s )

x = 20 m

 
18. 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) 15 m
c) 20 m
From the previous problem, we know it is in the air for t = 4.0 s

How far horizontally does it travel in this time?

x = v t

x = ( 5 m/s ) ( 4 s )

x = 20 m

d) 40 m


19. Consider two children on a playground merry-go-round. One is near the center and one is near the edge. The child near the edge

a) requires more time to make one revolution than
b) travels slower than
c) requires less time to make one revolution than
d) makes one revolution in the same time as the child near the center.

20. If a Ferris wheel has a radius of 10 m and requires 20 seconds to make a revolution, what is the linear speed of a passenger? C = 2 ÷ r; ÷ = 3.14

a) 0.78 m/s
b) 1.57 m/s
c) 3.14 m/s

v = ( 2 ÷ r ) / (20 s)

v = [ 2 (3.14) (10 m) ] / ( 20 s )

v = 62.8 m / 20 s

v = 3.14 m/s

d) 9.80 m/s

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."
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.
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 acceleration of an object.

 
25. The weight of an object is

a) another name forthe mass of an object.
b) the sum of all the forces on an object.
c) the force of gravity on an object.
d) always greater than the mass, even in a vacuum.

 
26. The net force on a 10-kg object, at rest, is

a) 98 N
b) 49 N
c) 10 N
d) zero; The net force on any object at rest must be zero!

 
27. The net force on a 10-kg object, in free fall, is

a) 98 N
F = ma

F = (10 kg) (9.8 m/s2 )

F = 98 N

b) 49 N
c) 10 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
The rope only pulls up on Harry once and the force up must equal the force down.

c) 250 N
d) 25 N

 
29. A force of 24 N acts on an object whose mass is 6 kg. This causes the object to accelerate at

a) 2 m/s2
b) 3 m/s2
c) 4 m/s2
F = m a

24 N = ( 6 kg ) a

a = 4 m/s2

d) 6 m/s2
 

30. A car, with mass of 1,000 kg, accelerates at 3 m/s2. The net force exerted on the car must be

a) 333 N
b) 1,000 N
c) 1,500 N
d) 3,000 N
F = m a

F = ( 1,000 kg ) ( 3 m/s2 )

F = 3,000 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
w = m g

w = ( 1,000 kg ) ( 10 m/s2 )

w = 3,000 N


32. What is the mass of a fireman whose weight is 500 N?

a) 9.8 kg
b) 25 kg
c) 50 kg
w = m g

500 N = m ( 10 m/s2 )

50 kg = m

d) 500 kg

33. A fireman, whose weight is 500 N ( m = 50 kg from the previous question), slides down a pole with an acceleration of 1 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) 50 N
b) 150 N
c) 450 N
When we write Newton's Second Law,
F = m a

the "F" in that equation is always the net force

Fnet = m a = ( 50 kg) ( 1 m/s2 )

Fnet = 50 N

What forces make up this net force?

Fnet = Fgravity - Ffriction
Fgravity = w = 500 N

50 N = 500 N - Ffriction

Ffriction = 450 N

d) 550 N

 

34. 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 down on the accelerator. Where does the ball land relative to the car?

a) behind the car
b) back into the car
c) in front of the car


35. 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 mast.
b) at the base of the mast.
c) behind the base of the mast.

 
36. 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.

 
37. Galileo

a) may be called the Father of Modern Optics.
b) wrote his findings in common Italian while at the University of Paducah.
c) may be called the Father of Modern Science.
d) wrote his findings about Gravity and discovered calculus.

 
38. 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.
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).

39. When an object moves in a circle, Newton's Second Law of Motion, F = ma, says that object must have a net force on it

a) only if its speed is changing.
b) directed toward its forward motion.
c) in the upward direction.
d) directed toward the center of the circle.


40. What value will the spring scale read in the system shown here?

a) zero
b) 50 N
c) 100 N
d) 200 N

41. In the sketch here, what value will the scale read if the little girl's weight is 250 newtons.

a) zero
b) 125 N
That is one-half her weight. The cord pulls up with that force on her left hand and on her right hand. The sum of the forces up equals the force of gravity pulling down.

c) 250 N
d) 500 N


42. The four fundamental forces are

a) gravity, friction, electricity, and atomic
b) gravity, electromagnetic, strong nuclear, and weak nuclear
c) gravity, strong electric, weak electric, and atomic
d) gravity, friction, air resistance, and atomic

43. “Projectile motion” describes the two-dimensional motion of an object under the influence of gravity. The path that such an object takes is known as

a) an ellipse.
b) a hyperbola.
c) a parabola.
d) a semi-circle.

 
44. A moving object on which no forces are acting will continue to move with constant

a) acceleration.
b) velocity.
c) centriptel acceleration.
d) displacement.

45. Sir Isaac Newton and Baron Gottfried Wilhelm von Liebnetz had a controversy over which of them had discovered or invented

a) Rubick’s Cube.
b) Euclid’s Geometry.
c) calculus.
d) algebra.

 
46. Weight is the force of gravity on an object. The weight of a one-kilogram mass is

a) 2.2 newtons.
b) 5.6 newtons.
c) 9.8 newtons.
d) 19.6 newtons.

47. A stone is dropped (from rest) from a bridge, high above a river. The stone takes five seconds before it hits the river. How fast is it going when it hits the water?

a) 5 m/s
b) 10 m/s
c) 50 m/s
vy = g t

vy = ( 10 m/s2 ) ( 5 s )

vy = 50 m/s

d) 100 m/s

48. A stone is dropped (from rest) from a bridge, high above a river. The stone takes five seconds before it hits the river. How high is the bridge above the water?

a) 10 m
b) 25 m
c) 125 m
y = (1/2) g t2

y = (1/2) ( 10 m/s2 ) ( 5 s )2

y = (1/2) ( 10 m/s2 ) ( 25 s2 )

y = 125 m

d) 250 m

 

 

49. 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
As with question 17, first we must ask "how long is it in the air?"
y = y + vyi + (1/2) ay t2 is somewhat difficult to solve. An easier approach is to use

vy = vyi + ay t

When it gets back to the level surface, vy = - vyi

- 15 m/s = 15 m/s + ( - 10 m/s2 ) t

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

3 s = t

d) 4.0 s
 

50. 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
From the previous question, we know the ball is in the air for t = 3.0 s

How far, horizontally, does it travel in that time?

The horizontal motion is at contstant velocity

x = v t

x = ( 8 m/s ) ( 3 s )

x = 24 m/s

d) 48 m


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