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physics 1020 > midterm > Flashcards

midterm Flashcards

1
Q

physics predicts how nature will behave in one situation based on what?

A

results of experimental data obtained in another situation

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2
Q

what are the SI units

A

meter: unit of length
kilogram: unit of mass
second: unit of time
kelvin: unit of temperature

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3
Q

how were seconds defined?

A

time for 9 192 631 770 cycles in the hyperfine transition in the ground state of Cs-133

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4
Q

how was the meter defined?

A

distance light travels in 1/299 792 458 seconds

-originally defined to give 10 000 km from equator to North pole through Paris

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5
Q

how was the kg defined?

A
  • mass of a special cylinder in paris

- mass of 1L of water

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6
Q

how do we represent units in terms or upper case/lower case letters?

A
  • lower case for all units: meter,joule, newton
  • lower case for symbols: m, s
  • upper case upright symboles derived from names: W, J, N
  • upper case sometimes used for L
  • no esses (for plural), no periods
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7
Q

dimension - def

A

refers to the physical nature of a quantity and the type of unit used to specify this quantity

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8
Q

scalar - def.

A
  • a scalar is just a number (magnitude) - no direction
  • ex: temperature, mass, time, length, energy

-use italic symboles to represent scalars

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9
Q

vector - def.

A
  • a vector is used to represent a physical quantity that must be described by both a magnitude and a direction
  • ex: it is not enough to throw the ball a correct distance, it must also be thrown in the correct direction

-use bold symbols to represent vectors or put an arrow over top of the symbol

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10
Q

when drawing vectors, the length of the arrow represents the ____ whereas the direction of the arrow is the _____

A

magnitude, direction of the vector

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11
Q

vectors and scalars can both be added and subtracted in the same way

true or false?

A

false, they can both be added, but not in the same way

  • when adding/subtracting vectors, direction of vectors must be taken into consideration as well as the magnitude
  • when two vectors are added/subtracted, the resultant is also a vector
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12
Q

what are the two properties of vector addition?

A

1) commutative - resultant is the same when added in any order
2) associative - the same result whatever their grouping, as long as their order remains the same

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13
Q

you can multiply a vector by a scalar

true or false?

A

true,
-if the scalar is a positive number, just multiply the magnitude of the vector by the scalar and do not change the direction

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14
Q

what does “i ‘hat’” represent?

A

is a vector of magnitude 1 and no dimensions, which lies parallel to the positive x axis

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15
Q

what does “j ‘hat’” represent

A

a vector of magnitude 1, and no dimensions, which lies parallel to the positive y axis

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16
Q

kinematics - def

A

the description of motion without reference to forces

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17
Q

dynamics - def

A

the effect forces have on motion

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18
Q

displacement

A
  • delta x
  • vector
  • all information about the direction is contained in the sign, it is a measure in one dimension
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19
Q

is average speed a vector or a scalar?

A

scalar

average speed = distance traveled/elapsed time

  • speed and velocity are different
  • relative to distance
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20
Q

is average velocity a vector or a scalar?

A
  • vector

- relative to displacement

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21
Q

acceleration - def

A

change in velocity over time

  • average acceleration = V-Vo / delta t
  • SI unit is m/s (2)
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22
Q

what are the 4 equations for constant acceleration in 1-D

A 
v = v0 + at
x = x0 + 1/2(v0+v)t
x = x0 + v0t +  1/2 at^2
v^2 = v0^2 + 2a(x- x(0))
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23
Q

gravity

A
  • objects fall toward the centre of Earth with acceleration independent of mass
  • if we neglect air resistance
  • near Earth’s surface, a is almost independent of height
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24
Q

what is the velocity of an object when it reaches the top of it’s projectile in projectile motion?

A

0 m/s

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25
Q

if you drop an object, in the absence of air resistance, it accelerates downward at 9.8 m/s^2. If instead you throw it downward, its downward acceleration after release is what?

A

9.8 m/s^2

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26
Q

a person standing at the edge of a cliff throws one ball straight up and another call straight down at the same initial speed. Neglecting air resistance, the ball to hit the ground below the cliff with the greater speed is which one?

A

-neither, they hit at the same time

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27
Q

average velocity is the same as instantaneous velocity in which case?

A

when velocity is constant

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28
Q

______ is the vector from initial to final position

A

displacement

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29
Q

average velocity points the same direction as the displacement

true or false?

A

true

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30
Q

if an object is moving around a circular path at a constant speed, is there a change in velocity?

A

yes, velocity is a vector and therefore if there is a change in direction there is a change in velocity

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31
Q

a truck drives due S for 1.2 km in 1.5 minutes. Then, the truck turns and drives 1.2 km due E for 1.5 minutes. Which one of the following statements is correct?

a) the ave. speed for the 2 segments is the same. The ave. velocity for the 2 segments is the same
b) the ave. speed for the 2 segments is not the same. The ave. velocity for the 2 segments is the same.
c) the ave. speed for the 2 segments is the same. The ave. velocity for the 2 segments is not the same
d) the ave. speed for the 2 segments is not the same. The ave. velocity for the 2 segments is not the same

A

C

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32
Q

superposition - def

A

if an object is subjected to two separate influences, each producing a characteristic type of motion, it responds to each without modifying its response to the other

  • Galileo
  • that is, we consider x and y motion separately
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33
Q

x and y motion are dependent on each other

true or false?

A

false

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34
Q

a toy rocket is launched at an angle of 45 degrees with a speed V0. If there is no air resistance, at what point during the time that it is in the air does the speed of the rocket equal 0.5 V0?

A

at no time during the flight

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35
Q

a _____ is a push or pull

A

force

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36
Q

____ forces arise from a physical contact

A

contact

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37
Q

_____ forces do not require contact and include gravity and electrical forces

A

action-at-a-distance

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38
Q

______ is a measure of the amount of stuff contained in an object

A

mass

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39
Q

inertial reference frame - def

A
  • a reference frame in which the law of inertia holds
  • requires ability to identify a free object: if no force acts on a body, a reference frame in which it has no acceleration is an inertial frame
  • does not hold on a carousal, or an accelerating car
40
Q

what is Newton’s first law?

A

law of inertia

-a free object moves with constant velocity at rest or in motion in a straight line

41
Q

what is Newton’s second law?

A

F = ma

  • force is also equal to the change in momentum over time
  • F = m (delta v/ delta t) = ma
42
Q

mass - def.

A
  • quantity of matter
  • quantity that determines weight (gravitational mass) (determined with a balance)
  • quantity that resists acceleration (inertial mass)
43
Q

what is the relationship between mass and acceleration?

A

mass is inversely proportional to acceleration

44
Q

force - def.

A
  • push or pull
  • disturbs “natural” state: causes acceleration
  • defines 1 N as the force required to accelerate 1 kg by 1 m/s^2
45
Q

what is the relationship between force and acceleration?

A

force is proportional to acceleration

46
Q

what are the 3 types of forces?

A

1) gravity
2) electroweak (electromagnetic and weak nuclear)
3) strong nuclear

47
Q

what is Newton’s third law?

A

for every action, there is an equal and opposite reaction

-change in momentum for the isolate system is 0

48
Q

what is Newton’s 4th law?

A

-law of gravitation

F = G (m1m2/r^2)

  • where G = 6.673x10^-11 Nm^2/kg^2
  • r = some distance
49
Q

how often are gravitational mass and inertial mass equal?

A

measured to be equal to at least one in 10^8

50
Q

weight - def.

A

-force due to earth’s (or a planet’s) gravity

W = mg, where g = 9.8 m/s^2

51
Q

normal force - def.

A

perpendicular force of the surface on an object

52
Q

friction - def

A
  • parallel force of a surface on an object (between surfaces)
  • resists motion - opposite to direction of the motion or applied force
  • material dependent (coefficient of friction)
  • friction DOES NOT cause motion
53
Q

kinetic friction - def

A
  • opposes sliding motion
  • amount of friction depends on how hard two surfaces are rubbing together
  • dependent on NORMAL FORCE
  • higher normal force = higher frictional force
54
Q

static friction - def

A
  • constraint
  • no motion
  • when the applied force is equal or lesser than the frictional force
  • static frictional force will scale up to some value until an object starts moving
55
Q

tension - def

A

force exerted by rope or cable

  • for an ideal line, the same force is exerted at both ends
  • objects connected by a taut line have the same acceleration
56
Q

pulley - def

A
  • changes the direction of a force
  • for an ideal pulley, the magnitude of the tension is the same on both sides
  • magnitude of acceleration of connected objects is the same
57
Q

equilibrium means ____ acceleration

A

0

-balanced forces in x and y directions

58
Q

in uniform circular motion, velocity and speed are constant

true or false?

A

false, speed is constant but velocity is always changing due to the changing direction of acceleration (always pointing to the center of the circle)

59
Q

Period (T) - def

A

the time it takes to complete one revolution of a circle

60
Q

the velocity vector in uniform circular motion is ____ to the path

A

tangent

61
Q

the direction of the centripetal acceleration is the same direction of velocity. in the limit that theta becomes very small, v points to the centre of the circle

true or false?

A

true

62
Q

two cars, with the same constant speed, are travelling through turns that have different radii (one is smaller). Which statement is trie about the magnitude a of each car?

a) a is larger for the car with the smaller r
b) a is smaller for the car with the smaller r
c) they are both the same, since both cars are moving at constant speed

A

a)

63
Q

in uniform circular motion, what direction does the force point?

A

toward the centre of the circle (radially inwards)

  • the centripetal force is the vector sum of all the force components pointing radially inward
  • direction of centripetal force is constantly changing
64
Q

centripetal acceleration can be produce by real or imaginary forces

true or false?

A

false, a real force is required to produce centripetal force

-ex: gravity, friction/normal force, tension

65
Q

a car goes around an un-banked curve, and the centripetal force is equal to the static frictional force, why?

A

-without friction, the car would slide out of the curve, static friction opposes the direction of this sliding

66
Q

on a frictionless banked curve, the centripetal force is the component of the _____ that points inward

A

normal force

67
Q

if speed is doubled (uniform centripetal motion), what happens to the centripetal force?

A

if speed doubles, centripetal force goes up by a factor of 4

equation: Fc = mv^2/r

speed is squared in the equation

68
Q

how can you provide a sense of weight in a satellite, where there is no gravity?

A
  • spin the satellite
  • person is moving in a circular orbit about the centre of the satellite, there must be a force to provide the centripetal acceleration
  • this force would be calculated to equal the weight on earth (mg)
69
Q

in circular motion (ball on a string for ex), if T = 0 at the top of the circle, what provides the centripetal acceleration?

A

all of the centripetal acceleration at that point is provided by the weight
-at this point, the orbital speed is at its minimum

70
Q

when is the minimum orbital speed of an object in centripetal motion? maximum speed?

A

minimum speed is at the top of the circle (when T = 0 and all centripetal acceleration is provided by the weight)

maximum speed is at the bottom of the circle

71
Q

vertical circular motion is also considered uniform motion

true or false?

A

false, not uniform motion since the speed is changing

-the net force is not always towards the center

72
Q

work - def

A

produces a change in energy of a system by the application of a force through a distance
-with a displacement of 0, there is no work done

W = Fs

73
Q

is work a scalar or a vector?

A

scalar

74
Q

only the force parallel to the displacement does work

true or false?

A

true

75
Q

what are the three situations in which work is equal to 0?

A

1) if the displacement is 0
2) if the force is 0
3) if the force is perpendicular to the displacement

76
Q

how can you get negative work? give examples

A

if the force is in the opposite direction of the displacement
-ex: frictional force, deceleration

77
Q

a person pulls a block up an inclined plane at a constant speed. The block moves 1 m along the plane and the tension force acting on the block is parallel to the plane. The coefficient of friction is 0.20. Which of these forces acting on the block do zero work on the block?

A

normal force

-it is perpendicular to the displacement

78
Q

work-energy theorem

A

if as a result of work on an object (system) the only change is its resulting motion:

W = (delta)KE = KEf - KEi

Wnet = KEf - KEi = 1/2mvf^2 - 1/2mvi^2

79
Q

what are the two work-energy theorem qualifications? (conservative forces only)

A

1) force is the net force on the object (system)
2) no internal changes to object (system)

ex: lifting a rock produces no kinetic energy because there is no NET force on the rock (on average) (i.e. positive work to pick up rock, 0 work when it’s in constant motion (no force), negative work when you decelerate it to reach the top)
ex: compression a spring produces no kinetic energy because there are internal changes to the system

80
Q

lifting an object produces kinetic energy

true or false?

A

false, it does not produce kinetic energy, rather, it changes the configuration (location) of the earth/object system

  • changes kinetic energy into potential energy
  • kinetic energy is only gained if the rock is released
81
Q

potential energy - def

A

energy stored in the configuration of interacting objects
-change in potential energy is the work done if there are no other changes in the system

(delta)PE = W(ext) = mgh

82
Q

how do we determine the position of zero PE?

A

it is arbitrary - we can choose where it is

-only the change in energy is of interest

83
Q

work done by a conservative force is irreversible

true or false?

A

false, it is reversible

84
Q

work done by a conservative force is dependent of the path

true or false?

A

false, it is independent of path

85
Q

work done by a conservative force in a closed loop is ____

A

zero

-ex: gravity, spring, electromagnetic - all fundamental forces, any force determined by the configuration of a system

86
Q

a _______ force does no work on an object moving around a closed path, starting and ending at the same point

A

conservative

87
Q

work done by _____ is ALWAYS negative, why?

A

friction

  • it ALWAYS opposes motion
  • friction is a non-conservative force and takes energy out of a system
  • same with air resistance
88
Q

work-energy theorem with conservative and non-conservative forces

A

Wnc = (delta) KE + (delta) PE

89
Q

what are the two statements of the work-energy theorem? (non-conservative and conservative forces)

A

1) work done by the net force
- Wnet = (delta) KE

2) work done by non-conservative forces
- Wnc = (delta) KE + (delta) PE

90
Q

mechanical energy

A

Total mechanical energy

E = KE + PE

Work energy theorem:

Wnc = (delta) PE + (delta) KE = (delta) E

if the work done on an object by non-conservative forces is 0, then the total mechanical energy is constant (conserved)

Ef = Ei

91
Q

the total _____ energy (E = KE + PE) of an object remains constant as the object moves, provided that the net work done by ______ forces is zero

A

mechanical, external non-conservative

92
Q

average power - def

A

the rate at which work is done (W) (J/s)
-force needs to be along the same line as the displacement

P = (delta) E/ (delta) t

93
Q

the principle of conservation of energy

A

energy can neither be created nor destroyed, but can only be converted from one form to another

other forms include: heat, chemical energy, mass energy

94
Q

impulse -def

A

-related to the change in momentum

J = Ft

(delta) p = m(vf - vi)

95
Q

impulse-momentum theorem equation

A

F (delta) t = (delta) p

physics 1020 (1 decks)

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