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Physics 101 > Exam 2 > Flashcards

Exam 2 Flashcards

1
Q

What is the equation for centripetal (radial) acceleration?

A

a(R) = v^2/r

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2
Q

The direction of the force needed to keep an object revolving in a circle is pointed

A

toward the center of the circle

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3
Q

What is the equation for the magnitude of the gravitational force

A

F(G) = G(m1m2/r^2)
m1 and m2: the masses of the two particles
r: distance between them
G: 6.67 x 10^-11 N*m^2/kg^2

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4
Q

What is the equation for the period (T) of an object revolving around a circle?

A

T = 1/f

f: frequency

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5
Q

What is the equation for the net force in the radial direction (circular motion) that acts on an object?

A

∑F(r) = ma(R) = m(v^2/r)

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6
Q

T or F? There is no outward force on a revolving object

A

T

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7
Q

The gravitational force F(grav) or F(G) exerted by the Earth on any object decreases with the ____ from the Earth’s center

A

square of its distance r

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8
Q

What is the equation for the acceleration of gravity at the Earth’s surface?

A

g = G(m(E)/r(E)^2)

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9
Q

What is the mass of Earth (m(E))?

A

m(E) = 5.98 x 10^24 kg

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10
Q

What is Kepner’s first law?

A

The path of each planet around the Sun is an ellipse with the Sun at one focus

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11
Q

What is Kepner’s second law?

A

Each planet moves so that an imaginary line drawn from the Sun to the planet sweeps out equal areas in equal periods of time

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12
Q

What is Kepner’s third law?

A

The ratio of the squares of the periods T of any two planets revolving around the Sun is equal to the ratio of the cubes of their mean distances from the Sun
(T1/T2)^2 = (s1/s2)^3
T1 and T2: periods (time needed for one rev around the Sun)
s1 and s2: mean distances from the Sun

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13
Q

Equation for velocity of circular motion?

A

v = 2πr/ T

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14
Q

Newton’s laws are causal laws. This means that

A

one occurrence can causes another

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15
Q

Energy and momentum are

A

conserved

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16
Q

Work and energy have no ___ associated with them

A

direction

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17
Q

What does work describe?

A

what is accomplished when a force acts on an object, and the object moves through a distance

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18
Q

What is the equation for work?

A

W = F||d

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19
Q

What is another equation for work?

A

W = Fd cosθ

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20
Q

What is the unit for work?

A

joule

1 J = 1 N * m

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21
Q

You need both a ___ and a ___ to do work

A

force; displacement

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22
Q

When a particular force is perpendicular to the displacement,

A

no work is done by that force

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23
Q

What is the equation for translational kinetic energy?

A

KE = 1/2mv^2

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24
Q

What is the equation for net work?

A 
W(net) = 1/2mv2^2 - 1/2mv1^2
W(net) = ΔKE
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25
Q

What does the work energy principle state?

A

the net work done on an object is equal to the change in the object’s kinetic energy

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26
Q

If positive net work (W) is done on an object, the object’s kinetic energy

A

increases by an amount W

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27
Q

If negative net work (W) is done on an object, the object’s kinetic energy

A

decreases by an amount W

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28
Q

Energy is measured in

A

joules

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29
Q

What is the formula for external work?

A

W(ext) = mg(y2-y1)

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30
Q

What is the formula for gravitational potential energy?

A

PE(G) = mgy

mg: object’s weight
y: height above some reference level

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31
Q

What is the change in gravitational potential energy?

A

equal to the negative of the work done by gravity

ΔPE(G) = -W(G)

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32
Q

What is the equation for elastic potential energy?

A

PE(el) = 1/2kx^2

k: spring stiffness constant
x: final amount stretched

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33
Q

What is characteristic of conservative forces?

A

work done does not depend on the path taken but only on the initial and final positions

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34
Q

What is characteristic of nonconservative forces?

A

work done depends on the path taken

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35
Q

Potential energy can only be defined for a ___ force

A

conservative

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36
Q

net work is the sum of

A

work done by conservative forces and nonconservative forces

W(net) = W(C) + W(NC)

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37
Q

What is the equation for conservation of mechanical energy?

A

KE2 + PE2 = KE1 + PE1

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38
Q

If only conservative forces do work, mechanical energy is

A

conserved

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39
Q

What is the equation for total mechanical energy (gravity only)?

A

1/2mv1^2 + mgy1 = 1/2mv2^2 + mgy2

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40
Q

What is the equation for total mechanical energy (elastic PE only)?

A

1/2mv1^2 + 1/2kx1^2 = 1/2mv2^2 + 1/2kx2^2

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41
Q

Work is done when

A

energy is transferred from one object to another

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42
Q

What are dissipative forces?

A

forces that reduce mechanical energy but not total energy

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43
Q

What is the equation for total mechanical energy (when friction is acting)?

A

1/2mv1^2 + mgy1 = 1/2mv2^2 + mgy2 + F(fr)d

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44
Q

What is the equation for power?

A

P = w/t

w: work
t: time

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45
Q

One horsepower equals

A

746 watts

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46
Q

Power is measured in

A

watts

47
Q

Another equation for power involving net force?

A

P(ave) = Fv(ave)

48
Q

What is efficiency?

A

the ratio of the useful power output of the engine (P(out)), to the power input, (P(in))
e = P(out)/P(in)

49
Q

What is the equation for momentum?

A

p = mv

50
Q

The direction is momentum is ___ the momentum of the velocity

A

the same as

51
Q

What is the unit of momentum?

A

kg x m/s

52
Q

The more momentum an object has

A
  • the harder it will be to stop it

- the greater effect it will have on another object if it is brought to rest by striking that object

53
Q

What does Newton’s Second Law state?

A

the rate of change of momentum of an object is equal to the net force applied to it

54
Q

What is the equation of net force that involved change in momentum?

A

ΣF = Δp/Δt

55
Q

What is the equation for the conservation of momentum when there is no net external forces acting on a system?

A

mAvA + mBvB = mAvA’ + mBvB’

56
Q

What does the law of conservation of momentum state?

A

the total momentum of an isolated system of objects remains constant

57
Q

What is an impulse?

A

a change in momentum

impulse = FΔt

58
Q

What is the equation for the law of conservation of total kinetic energy for an elastic collision?

A

1/2mAvA^2 + 1/2mBvB^2 = 1/2mAvA’^2 + 1/2mBvB’^2

59
Q

In an inelastic collision

A

kinetic energy is not conserved

60
Q

What is the equation for a head on elastic collision?

A

vA - vB = -(v’A - v’B)

61
Q

For any elastic head-on collision, the relative speed of two objects after the collision ___ as before the collision, no matter what the masses are

A

has the same magnitude (but opposite direction)

62
Q

If two objects stick together as a result of a collision, the collision is said to be

A

completely inelastic

63
Q

What is the center of mass?

A

the one point of an object that moves in the same path that a particle would move

64
Q

What is the equation for the x coordinate of the center of mass?

A

x(CM) = (mAxA + mBxB)/(mA + mB)

65
Q

If one mass is greater than the other, the CM

A

is closer to the larger mass

66
Q

What is the y coordinate for the center of mass?

A

y(CM) = (mAyA + mByB)/(mA + mB)

67
Q

Center of mass and center of gravity are

A

the same thing

68
Q

What is the equation of Newton’s Second Law for a system?

A

Ma(CM) = Fnet
M: total mass of the system
a(CM): the acceleration of its center of mass of the system

69
Q

What is meant by “purely rotational motion”?

A

that all points in the object move in circles, and that the center of these circles all lie on one line called the axis of rotation

70
Q

What is the equation for θ in radians?

A

θ = l/r

r: radius of circle
l: the arc length subtended by the angle θ

71
Q

How many radians does one revolution equal?

A

1 rev = 2Π radians

72
Q

What is the equation for angular displacement?

A

Δθ = θ2 - θ1

73
Q

What is the equation of average angular velocity?

A

ω(ave) = Δθ/Δt

74
Q

What are the units for angular velocity?

A

radians per second (rad/s)

75
Q

What is the equation for average angular acceleration?

A

α(ave) = Δω/Δt

76
Q

How are linear velocity (v) and angular velocity (ω) related?

A

v = rω

77
Q

How are angular acceleration and linear acceleration related?

A

a(tan) = rα
a(tan): linear acceleration
α: angular acceleration

78
Q

The total linear acceleration of a point is the sum of

A

the radial (centripetal) acceleration and the linear acceleration
a = a(tan) + a(R)
a(tan): linear acceleration
a(R): radial (centripetal) acceleration

79
Q

What is the relationship between centripetal acceleration and angular velocity?

A

a(R) = ω^2r

80
Q

Centripetal acceleration is ___ the farther you are from the axis of rotation

A

greater

81
Q

What is the relationship between angular velocity and frequency?

A

ω = 2Πf

82
Q

What is the unit for frequency?

A

Hertz (1 Hz = 1 rev/s)

83
Q

What is the equation for the velocity of an object that is rolling without slipping?

A

v = rω

84
Q

Angular acceleration is proportional to the

A

product of the force times the lever arm (torque)

85
Q

What are the two equations that can describe torque?

A 
τ= r⊥F
τ= rFsinθ
86
Q

mr^2 represents an object’s

A

moment of inertia (Ι)

87
Q

When a mass is concentrated farther from the axis of rotation, the rotational inertia is

A

greater

88
Q

Rotational kinetic energy can be expressed by

A

1/2Ιω^2

89
Q

What are the units for rotational kinetic energy?

A

joules

90
Q

Total kinetic energy equals

A

KE = 1/2Mv(CM)^2 + 1/2I(CM)ω^2

91
Q

What is the equation for the work done by torque?

A

W = τΔθ

92
Q

What is the equation for the power of torque?

A

P = τω

93
Q

What is the equation for angular momentum (L)?

A

L = Iω

94
Q

What does the law of conservation of angular momentum state?

A

the total angular momentum of a rotating object remains constant if the net torque acting on it is zero

95
Q

Which of the following statements is NOT TRUE about work done on a laptop as a student moves it by sliding from one side of a desk to the other?
-The normal force exerted by the desk on the laptop does no work.
-The force of friction does negative work.
-The net work is zero.
-The force of gravity does positive work.
The work done by the student is positive.

A

The force of gravity does positive work.

96
Q

A conveyor moves a carton up an incline at constant speed from the first floor to the second floor of a factory. Pick the statement below which is true.

  • The normal force acting on the carton does work.
  • The force of friction acting on the carton does no work because the carton is not sliding.
  • The work done on the carton by the force of gravity does not depend on the angle of the incline.
  • The work done by the force of friction depends on the speed of the conveyor.
A

The work done on the carton by the force of gravity does not depend on the angle of the incline.

97
Q

Two satellites follow circular orbits about the earth. The orbital radius of Satellite 1 is 4 times the orbital radius of Satellite 2. The mass of Satellite 1 is twice the mass of Satellite 2. All but one of the following statements is true. Pick the statement which is FALSE.

  • The speed of Satellite 1 is half the speed of Satellite 2.
  • The gravitational force acting on Satellite 2 is 8 times greater than the gravitational force acting on Satellite 1.
  • The centripetal accelerations of Satellites 1 and 2 are independent of their respective masses.
  • The centripetal acceleration of Satellite 1 is one eighth the centripetal acceleration of Satellite 2.
A

The centripetal acceleration of Satellite 1 is one eighth the centripetal acceleration of Satellite 2.

98
Q

Which of the following statements is INCORRECT?

  • The power delivered to a falling rock by the gravitational pull of the earth increases as the speed of the rock increases.
  • Power has the units of energy.
  • Power is the rate at which work is being done.
A

Power has the units of energy.

99
Q

Which of the following statements is incorrect in the case that one or more non-conservative forces is acting on a system?

  • Total energy is conserved.
  • The mechanical energy of the system is conserved.
  • The thermal energy of the system may be changing.
  • The net work done by non-conservative forces depends on the path followed by the system
A

The mechanical energy of the system is conserved

100
Q

If there are no non-conservative forces acting on a system, which of the following quantities is conserved?

A

mechanical energy

101
Q

The net work done on a crate as it is sliding down a ramp is zero. Which of the following statements always holds?

  • A worker must be applying a force on the crate which has a component in the direction up the ramp in order to keep the crate from accelerating.
  • The work done by the force of friction is positive.
  • The work done by the force of gravity is negative.
  • The net work is zero because the normal force is doing no work.
  • The crate is sliding down the ramp at constant speed.
A

The crate is sliding down the ramp at constant speed.

102
Q

A ball is thrown straight up. Neglecting air resistance, which statement is NOT TRUE regarding the energy of the ball?

  • The kinetic energy decreases while the ball is going up.
  • The potential energy decreases while the ball is going up.
  • The potential energy decreases when the ball is coming down.
  • The sum of the kinetic energy and potential energy is constant.
  • The kinetic energy increases when the ball is coming down.
A

The potential energy decreases while the ball is going up.

103
Q

Two balls are thrown from the roof of Gallalee Hall. Both are thrown at the same speed, but Ball 1 is thrown horizontally and Ball 2 is thrown downward at an angle of 45 degrees below the horizontal. Which ball has the greater speed when it reaches the ground? Neglect air resistance.

  • Ball 2.
  • Both balls have the same speed.
  • Ball 1.
A

Both balls have the same speed.

104
Q

A constant net force is applied to Block 1. After it has been displaced a distance d, its speed is v. The same net force is then applied to Block 2 and after some displacement its speed is 2v. Block 2 is twice as massive as Block 1. How far was Block 2 displaced? (Both blocks start from rest.)

  • d/2.
  • d.
  • 8d.
  • 4d.
  • 2d.
  • d/4.
A

8d

105
Q

A fork lift is used to carry a loaded pallet up a ramp at a constant speed of 4 mph. If the operator were instead to drive the fork lift at 8 mph, how would the power delivered by the fork lift to the pallet change?

  • The power would quadruple because the kinetic energy would quadruple
  • The power would double because the rate at which energy is being delivered to the pallet by the fork lift would double.
  • The power would be the same because the force exerted by the fork lift is the same at both speeds.
  • The power would decrease by a factor of two because it would take half as long to climb the ramp.
A

The power would double because the rate at which energy is being delivered to the pallet by the fork lift would double.

106
Q

Which of the following statements is not correct?

  • In a collision between an insect and a truck, the insect exerts the same force on the truck as the truck exerts on the insect.
  • Another way of stating Newton’s Second Law is that the net force is equal to the rate at which momentum is changing.
  • In an inelastic collision, the total kinetic energy decreases.
  • Total momentum is conserved if the net external force acting on a system is zero.
  • Momentum is the product of mass and speed.
A

Momentum is the product of mass and speed.

107
Q

Two cars traveling in opposite directions at the same speed of 10 mph collide head-on. Immediately after the collision, the cars move together in the same direction as the first car but at 5 mph. Which of the following statements is correct?

  • Kinetic energy is conserved in the collision because the sum of the speeds of the cars after the collision is equal to the speed of the cars before the collision.
  • The second car is twice as heavy as the first car.
  • The first car is twice as heavy as the second car.
  • None of the statements can be judged correct or incorrect because not enough information is given.
  • The first car is three times as heavy as the second car.
A

The first car is three times as heavy as the second car.

108
Q

Two blocks, initially at rest, are each acted upon by the same net force over the same interval in time. At the end of the interval, Block 1 is moving twice as fast as Block 2. Which of the following statements is true?

  • The mass of Block 2 is half the mass of Block 1.
  • The force of friction acting on Block 2 is greater than the force of friction acting on Block 1.
  • The mass of Block 2 is twice the mass of Block 1.
  • Block 1 and Block 2 have the same kinetic energy at the end of the interval.
  • The average force acting on Block 1 is twice as great as the average force acting on Block 2.
A

The mass of Block 2 is twice the mass of Block 1.

109
Q

Which of the following statements is NOT CORRECT about an elastic collision between two objects?

  • The net external force on the two-object system is zero.
  • The two objects do not stick together as a result of the collision.
  • The direction of the relative velocity between the two objects after the collision is opposite the direction of the relative velocity before the collision.
  • The total kinetic energy of the two objects is the same before and after the collision.
  • In the case where the colliding objects have unequal masses and the heavier object is at rest before the collision, the direction of the lighter object is reversed by the collision.
  • The magnitude of the relative velocity between the two objects may change as a result of the collision.
A

The magnitude of the relative velocity between the two objects may change as a result of the collision.

110
Q

Which of the following statements is correct?

  • A ring and a uniform disk have the same mass and radius. They therefore have the same rotational inertia.
  • Two rings have the same mass but one ring has a diameter twice as large as the the other. The same force F is applied to each ring on the circumference of the ring and and in the direction tangent to the ring. -The smaller ring will experience the smaller angular acceleration.
  • The rotational inertia is independent of the location of the axis about which the rotation occurs.
  • The torque which a force exerts depends on the position at which the force is applied.
A

The torque which a force exerts depends on the position at which the force is applied.

111
Q

A disk undergoing constant angular acceleration starting from rest undergoes two complete revolutions in time t. The time it took for it to complete the first revolution is

  • More than t/2.
  • t/2.
  • Less than t/2.
  • unknown because not enough information is given.
A

More than t/2.

112
Q

Which of the following quantities is not required to calculate the buoyant force exerted by a fluid on an object partially submerged in it?

  • The density of the fluid
  • The acceleration of gravity
  • The fraction of the object’s volume submerged in the fluid
  • The density of the object
  • The volume of the object
A

-The density of the object

113
Q

Which of the following statements is not correct? Assume the fluid is incompressible.

  • If the pressure is increased at one point in a fluid, the pressure increases at every other point in the fluid by an amount which depends on the depth
  • The pressure in a fluid increases linearly with depth.
  • The upward force that a fluid exerts on an object submerged in it is equal to the weight of the fluid displaced by the object.
  • Pressure is force per unit area.
A

If the pressure is increased at one point in a fluid, the pressure increases at every other point in the fluid by an amount which depends on the depth

Physics 101 (1 decks)

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