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PHY101
Chapter Two Review
Newton’s Laws
Study of Newton’s
Laws
Basics of
Force
Newton’s
Laws
Analyzing
Forces
Circular Resistive
Potpourri
Motion
Forces
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Basics of Force
$100
What is Force?
ANSWER
Basics of Force
$200
What is the equation for force?
What are the units in the 3 systems?
ANSWER
Basics of Force
$300
What is weight?
ANSWER
Basics of Force
$400
What is momentum?
ANSWER
Newton's Laws $100
What is mass?
ANSWER
Newton's Laws
$200
What is Newton’s First Law?
ANSWER
Newton's Laws
$300
What is Newton’s 2nd Law?
ANSWER
Newton's Laws
$400
What is Newton’s 3rd Law?
ANSWER
Analyzing Forces
$100
What is a free body diagram?
ANSWER
Analyzing Forces
$200
What is a normal force?
ANSWER
Analyzing Forces
$300
What is Hooke’s Law?
ANSWER
Analyzing Forces
$400
A child stands on a bathroom scale while
riding in an elevator. The child's weight
when the elevator is not moving is 200 N.
What is the child’s mass in kg?
What does the scale read (tension T) when
the elevator accelerates upward at 1.00
m/s2?
ANSWER
Circular Motion
$100
If an object moves in a
circle, what kind of force
acts the centripetal force?
ANSWER
Circular Motion
$200
What is the equation for centripetal (radial) force?
ANSWER
Circular Motion
$300
What is Newton’s Law of Gravity?
ANSWER
Circular Motion
$400
What is the acceleration due to the earth's gravity at a distance
of one earth radius above the earth's surface?
a. 2.5 m/s²
b. 5 m/s²
c. 10 m/s²
d. 20 m/s²
ANSWER
Resistive Forces $100
What is a drag force?
ANSWER
Resistive Forces $200
What is friction?
ANSWER
Resistive Forces $300
Name two types of friction?
ANSWER
Resistive Forces $400
A horizontal force of 640 N is applied to a car with a
mass of 1600 kg. What is the acceleration of the car
if the coefficient of rolling friction is 0.01?
a. 0.02 m/s²
b. 0.03 m/s²
c. 0.2 m/s²
d. 0.3 m/s²
ANSWER
Potpourri $100
A 9.00-kg object is moving in a circle with a constant speed of 45.0 m/s.
If the circular path has a radius of 20.0 m, what is the net force on the
object?
ANSWER
Potpourri $200
What are the conditions for simple
harmonic motion?
ANSWER
Potpourri $300
Before going to the beach, you check
the position of the moon. Why?
ANSWER
Potpourri $400
The average orbital speed of Mars is 2.41 x 104 m/s.
If the radius of Mars's orbit is 2.28 x 1011 m, how long does it
take Mars to complete one orbit?
ANSWER
Basics of Force
$100
Answer
What is Force?
Force is a push or a pull.
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Basics of Force
$200
Answer
What is the equation for force?
Force = F = ma = mDv/Dt
SI unit
1 kg*m/s² = 1 Newton = 1 N
cgs unit
1 g*cm/s² = 1 dyne
Common unit 1 slug*ft/s² = 1 lb.
1 N = 105 dynes = 0.2248 lbs
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Basics of Force
$300
Answer
What is weight?
Weight is the force of gravity acting on a body.
W = mg where g is local gravity
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Basics of Force
$400
Answer
What is momentum?
Momentum is mass X velocity
p = mv Unit is 1 kg*m/s in SI
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Newton's Laws $100
Answer
What is mass?
Mass is a measure of an object’s resistance to
acceleration. It is a measure of the quantity of
matter in an object.
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Newton's Laws $200
Answer
What is Newton’s First Law?
An object will remain at rest or
in motion with a constant velocity
unless acted upon by an outside
force.
 F = 0 v = constant a = 0
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Newton's Laws $300
Answer
What is Newton’s 2nd Law?
An object is accelerated whenever a net
external force acts on it.
The net force
equals the objects mass times its
acceleration.
 F = ma
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Newton's Laws $400
Answer
What is Newton’s 3rd Law?
Forces always come in pairs. When one object
exerts a force on a second object, the second
exerts an equal and opposite force on the first.
 F = 0
F12 = -F21
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Analyzing Forces
$100
Answer
What is a free body diagram?
A free body diagram is a force picture showing all the forces, the
net acceleration and the direction of motion.
 Fy= ma = T - mg
T
a
T = mg + ma
T = m(g + a)
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mg
Analyzing Forces
$200
Answer
What is a normal force?
A normal force is a (reactive) balancing
force such that  F = 0.
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Analyzing Forces
$300
Answer
What is Hooke’s Law?
This is a conservative spring force equation.
F= - kSx = ma
where kS = Weight of spring & object/stretch
in SI units of N/m
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Analyzing Forces $400
Answer
A child stands on a bathroom scale while riding in an elevator.
The child's weight when the elevator is not moving is 200 N.
What is the child’s mass in kg? m = Weight/g = 20.4 kg
What does the scale read (tension T) when the elevator
accelerates upward at 1.00 m/s2?
 Fy= ma = T - mg
T = mg + ma
T = m(g + a) = 220 N
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Circular Motion $100
Answer
If an object moves in a circle, what
kind of force acts the centripetal
force?
A real force like tension or gravity
must act as a centripetal force and
point toward the center of the circle.
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Circular Motion $200
Answer
What is the equation for centripetal (radial) force?
F centripetal = mv²/r
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Circular Motion $300
Answer
What is Newton’s Law of Gravity?
F = G m1*m2/d²
G = 6.67 * 10-11 N*m²/kg²
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Circular Motion $400
Answer
What is the acceleration due to the earth's gravity at a distance
of one earth radius above the earth's surface?
a.
2.5 m/s²
b. 5 m/s²
c. 10 m/s²
d. 20 m/s²
F = G M*m/d² = mg
If dnew = 2d, then FNEW = G M*m/(4d²) = mgNEW = mg/4
gNEW = g/4 = 2.45 m/s²
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Resistive Forces $100
Answer
What is a drag force?
A resistive force called air resistance.
Drag Force = ½ C*density*Area*v²
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Resistive Forces $200
Answer
What is friction?
A force of resistance to relative motion
between 2 bodies or substances in physical
contact.
f = Coefficient of friction *Normal Force = µFN
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Resistive Forces $300
Answer
Name two types of friction?
Static friction no motion
40
Kinetic friction motion
Friction in N
35
30
25
20
15
10
5
0
0
10
20
30
40
Pull in N
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50
60
70
80
Resistive Forces $400
Answer
A horizontal force of 640 N is applied to a car with a mass of 1600 kg.
What is the acceleration of the car if the coefficient of rolling friction
is 0.01?
a. 0.02 m/s²
Fy = 0 = FN – mg
b. 0.03 m/s²
c. 0.2 m/s²
d. 0.3 m/s²
FN = mg = 15680 N fK = µFN = µmg = 157 N
FX = ma = Pull – fk = 640 N – 157 N = 483 N
a = FX /m = 483 N/ 1600 kg = 0.30 m/s²
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Potpourri $100
Answer
A 9.00-kg object is moving in a circle with a constant speed of 45.0 m/s.
If the circular path has a radius of 20.0 m, what is the net force on the
object?
F = mv²/r = (9.00kg)*(45 m/s)²/(20.0m) = 911 N
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Potpourri $200
Answer
What are the conditions for simple
harmonic motion?
1. Motion must be periodic
2. Force must cause the motion and be
parallel to it.
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Potpourri $300
Answer
Before going to the beach, you check the position of
the moon. Why?
Low tide = moon on horizon
High tide = high point in sky
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Potpourri $400
Answer
The average orbital speed of Mars is 2.41 x 104 m/s.
If the radius of Mars's orbit is 2.28 x 1011 m, how long does it
take Mars to complete one orbit?
V = 2pr/T
T = 2pr/v = 5.94 * 107 sec = 688 days
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