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SCI-111 Exam #1
Fall 2009
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ONONDAGA COMMUNITY COLLEGE
DEPARTMENT OF CHEMISTRY AND PHYSICAL SCIENCE
SCI 101: PHYSICAL SCIENCE I
Exam 1 Fall 2009 Solutions
(64 Points Total)
Name: _______________
Class Meeting Time___
__
Multiple Choice
Circle the BEST answer (20 Points: 20 questions @ 1 Point each)
1) According to the scientific definition of work, pushing on a rock accomplishes no work unless
there is
A) an applied force greater than its weight
D) movement in the same direction as the
B) a net force greater than zero
force
C) an opposing force
2) Power is
A) the rate at which energy is expended
B) work per unit of time.
C) the rate at which work is done
D) any of the above.
3) The potential energy of a box on a shelf, relative to the floor, is a measure of
A) the work done putting the box on the
C) the energy the box has because of its
shelf from the floor.
position above the floor.
B) the weight of the box times the distance
D) any of these.
above the floor.
4) Which quantity has the greatest influence on the amount of kinetic energy that a large truck has
while moving down the highway?
A) mass
C) velocity
B) weight
D) size
5) The metric unit of a joule (J) is a unit of
SCI-111 Exam #1
Fall 2009
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A) potential energy.
B) work
6) The law of conservation of energy is a statement that
A) energy must be conserved and you are
breaking a law if you waste energy.
B) the supply of energy is limited so we
must conserve.
7) Energy is
A) the ability to do work.
B) the work needed to create potential or
kinetic energy.
C) kinetic energy.
D) all of the above
C) the total amount of energy is constant.
D) energy cannot be used faster than it is
created.
C) the work that can be done by an object
with PE or KE.
D) all of the above.
8) How fast you are changing your speed or direction of travel is a property of motion known as
A) speed.
C) acceleration.
B) velocity.
D) none of the above.
9) Ignoring air resistance, an object falling toward the surface of the earth has an acceleration that is
C) decreasing.
A) constant.
B) increasing.
D) dependent on the weight of the object.
10) A Nm/s is a unit of
A) energy
B) power.
11) A ball rolling across the floor slows to a stop because
A) there are unbalanced forces acting on
it
B) the force that started it moving wears out
C) force.
D) work.
C) all the forces are balanced.
D) the net force equals zero.
12) The tendency of a moving object to remain in unchanging motion in the absence of an unbalanced
force is called
C) acceleration
A) inertia
B) free fall
D) impulse
13) A heavy object and a light object are dropped from rest at the same time in a vacuum. The heavier
object will reach the ground
A) before the lighter object
C) after the lighter object
D) It depends on the shape of the object
B) at the same time as the lighter object
14) A cannonball is fired straight up at 50 m/s. Neglecting air resistance, when it returns to its starting
point its speed
A) is 50 m/s.
C) is less than 50 m/s.
B) is more than 50 m/s.
D) depends on how long it is in the air.
.
SCI-111 Exam #1
Fall 2009
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15) With all other factors equal, if you double the mass of an object while a constant unbalanced force is
applied, the acceleration will be
A) doubled.
C) one-half as much.
B) increased fourfold.
D) one-fourth as much.
16) Which of the following is a unit that can be used for a measure of weight?
A) kilogram
C) kg  m/s
B) Newton
D) none of these
17) Which of the following is a unit for a measure of resistance to a change of motion?
A) lb
C) N
D) none of the above
B) kg
18) A tentative scientific explanation which may or may not be rejected upon further experimentation is
called a
A) theory.
C) model.
D) principle.
B) hypothesis.
19) What do you know for sure about the forces on the system of you and a bicycle as you pedal the bike
at a constant speed in a straight line?
A) The applied force you are exerting on
C) The resisting forces of friction are
the pedal is greater than other forces.
greater than the applied forces.
D) Air and tire friction forces are less than
B) All forces are in balance.
the applied force.
20) Which one of the following is not a fundamental property?
A) mass
C) weight
B) time
D) length
SCI 101 EXAM 1
Fall 2009
Essay Question
(10 points awarded based on completeness)
Imagine a bowling ball and a piece of notebook paper held at shoulder height. Each is released to
fall at the same time. Your experience tells you that the heavier object (i.e. the bowling ball) will
strike the ground well before the lighter object (i.e. the piece of notebook paper.). However, in
class you have been told that heavy and light objects accelerate equally in free fall, implying that
the bowling ball and the paper should strike the ground at the same time. Please clear up this
seeming contradiction. Explain what “free fall “is and why the bowling ball does strike the ground
first even though both the bowling ball and paper will accelerate equally in free fall. In other
words, why does the bowling ball strike the ground first if objects accelerate equally in freefall?
You may include diagrams to supplement your response.
 Objects falling near the surface of the Earth do not fall in free fall, but fall more slowly
due to air resistance (drag).
 Air resistance causes lighter objects to fall more slowly (accelerate less) than heavy
objects. (We all know that a sheet of paper falls slower than a bowling ball)
 In the absence of air resistance, heavy objects fall with the same acceleration of 9.8 m/s2
as light objects. (You can see this yourself by watching this You Tube video of an Apollo
15 astronaut dropping a feather and a hammer on the Moon.)
 Why does air resistance affect a lighter object more than a heavy object? Let’s examine
the NET FORCE on a heavy and light object falling hear the Earth’s surface.
o For simplicity, lets assume that the cross-sectional area of the paper and
bowling ball are about the same. If so then the drag forces would be about
equal also.
o A force diagram for each would look like this…
Drag Force
Bowling Ball
Styrofoam Sphere
Weight
BLUE arrows represent the
NET FORCE
SCI 101 EXAM 1
Fall 2009
 As you can see from the length of the force “arrows”, the drag force is about the same for
each sphere, but the weight forces are much different with the Bowling Ball having a
much greater weight than the paper. The NET FORCE is the difference between the
weight and the drag force. The NET FORCE on the Bowling Ball. is much greater than on
the paper
Bowling Ball
Paper
Let that mass of the Bowling Ball be
M, indicating a large mass.
The Net Force is the difference
between the downward weight and
the upward drag:
Let that mass of the paper, indicating
a small mass.
The Net Force is the difference
between the downward weight and
the upward drag:
FNET  Weight - Drag
FNET  Weight - Drag
 Mg  FDrag
From Newton’s 2 Law, the Net
force is the mass times the
acceleration:
ND
 mg  FDrag
From Newton’s 2ND Law, the Net
force is the mass times the
acceleration:
FNET  Ma
FNET  ma
Combining the two equations gives:
Combining the two equations gives:
Ma  Mg  FDrag
ma  mg  FDrag
a
Mg  FDrag
ag
The term
FDrag
M
a
M
FDrag
ag
M
will be small
because M is large. Thus the
acceleration of the Bowling Ball will
be close to the free fall value of g.
mg  FDrag
The term
FDrag
m
m
FDrag
m
will be large
because m is small. Thus the
acceleration of the paper be close to
zero.
Thus, the net acceleration of each object is g minus a term that is inversely proportional to
the mass . Sin the mass of the bowling ball is so much greater than the mass of the paper, this
“minus term” in the net acceleration is much smaller for the bowling ball. The bowling ball
accelerates downward at a value of nearly g, but the paper’s acceleration is much less than g.
SCI 101 EXAM 1
Fall 2009
Problems
(30 Points)
TO GET FULL CREDIT, YOU MUST SHOW ALL WORK
INCLUDING VARIABLES, EQUATIONS USED, UNITS, AND CONVERSIONS
1.
(a) What is the acceleration of a Ferrari that
moves from rest to a velocity of 108.0 km/h
in 4.50 seconds? (2 Pts)
(Report your answer in the common metric units for
acceleration.)
a
v

t
km
108.8  0.2778 m
s  6.67 m
hr 
4.50 s
4.50 s
s2
108.8
(b) Using your acceleration value from part (a), determine the net force (Fnet),
in Newtons (N), needed to cause that amount of acceleration if the car has a mass of
1500 kg? (2 Pts)
F  ma  1500 kg  6.67
m
 10,000 N
s2
3. A Canada goose has an average flight speed of 13.4
m/s (or equivalently 30 mph). How much time is
required for an average Canada goose to complete
its 2,413 km (or equivalently 1,500 mile) fall
migration? (2 pts)
x
t
x 2,413,000 m
t 

 180,074 s  50 hours
m
v
13.4
s
v
SCI 101 EXAM 1
Fall 2009
4. A ball dropped from a building falls for 5.00 seconds before it hits the ground.
(Ignore the effects of air resistance.)
a. How high is the building? (2 pts)
Free Fall problem,
d
1 2 1
m
at   9.8 2  5 s   122.5 m
2
2
s
SCI 101 EXAM 1
Fall 2009
5. Starting from rest, two skaters “push off” against each other on smooth level ice, where friction
is negligible. The female skater has a mass of 40 kg and moves away with a velocity of 3.0
m/s. The male skater has a mass of 48 kg. Find the recoil velocity of the male skater. (2
points)
Momentum Conservation Problem
pInitial  pFinal
pInitial  0
m
m
 48 kg  x
s
s
m
m
 0  40 kg  3.0  48 kg  x
s
s
m
40 kg  3.0
m
s  2.5 m
x 
s
48 kg
s
and
pFinal  40 kg  3.0
SCI 101 EXAM 1
Fall 2009
6a. How much work is done in lifting a 2,800 kg pallet of cement
bags from the ground to a storage area at a height of 4
meters? (2 pts)
W  F d
 mg  d
 2,800 kg  9.8
m
4m
2
s
 1019,760 J
6b. Using energy conservation, estimate the velocity the cement bags would have as they hit the
ground if they fell. (2 pts)
PELoss  KEGain
1 2
mv
2
2  PE
v 
m

v
2  109,760 J
2,800 kg
v  8.85
m
s
SCI 101 EXAM 1
Fall 2009