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Malika Physics MCAT > Kinematics > Flashcards

Kinematics Flashcards

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1
Q

The product of a vector and a scalar is a (vector/scalar).

A

ALWAYS a vector.

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2
Q

Differentiate vector vs. scalar

A

Vector - has direction & magnitude
Scalar - has only direction

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3
Q

State examples of vectors and scalars.

A

Vectors - velocity, displacement, acceleration, force, weight, momentum, electric field, magnetic field, torque, impulse, gravity
Scalars - mass, temperature, speed, work, energy, time, density

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4
Q

True or false:
The product of two vectors is always a vector.

A

False; the product of two vectors can sometimes be a scalar or a vector.

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5
Q

If the product of two vectors is a scalar, what equation do you use?

A

|A||B|cosθ

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6
Q

If the product of two vectors is a vector, what equation do you use?

A

|A||B|sinθ
*Make sure to determine the direction of the vector using the hand technique

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7
Q

Right hand rule

A

Used to determine the direction of a vector when getting the cross product (often used in torque)

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8
Q

Tip for subtracting vectors

A

Flip the direction of one of the vectors and line it up in parallel to other vector to determine the answer.

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9
Q

True or false:
Gravity is a vector

A

True

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10
Q

Define velocity and corresponding units

A

A measure of displacement (change in position) over time; m/s
On a displacement vs. time graph –> steeper positive slope = greater velocity
*Displacement can be negative

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11
Q

Define speed & corresponding units

A

A measure of distance traveled over time; m/s

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12
Q

Force and corresponding units

A

Any influence capable of causing a mass to accelerate; units: Newtons or (kg x m)/s2

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13
Q

On the MCAT, what does constant velocity or constant speed mean if used in the question?

A

1) No acceleration
2) No net force
3) All forces sum to zero (i.e., up forces = down forces, left forces = right forces, etc.)
4) No change in direction
5) The object is in equilibrium

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14
Q

Acceleration and corresponding units

A

The change in velocity over time
∆v/t
units: m/s2
Example: going from 0 mph to 40 mph in 10 seconds

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15
Q

Differentiate weight vs. mass

A

Weight - a measure of the gravitational force on a mass (unit: N)
Mass - a measure of a body’s inertia (unit: kg)

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16
Q

Equation for calculating weight

A

F = mass x gravitational force
F is weight
gravitational force is a constant 10 m/s2

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17
Q

If a person is walking at a constant velocity, the acceleration is _____.

A

0 m/s2

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18
Q

Equation for avg. velocity:

A

Avg. velocity = Δx/Δt

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19
Q

What is relative speed/velocity? How do you calculate it?

A

Objects moving opposite directions –> add the two velocities
Objects moving same direction –> subtract the two velocities

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20
Q

The maximum relative speed refers to when 2 objects move (opposite/same) directions.

A

Opposite

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21
Q

The minimum relative speed refers to when 2 objects move (opposite/same) directions.

A

Same

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22
Q

Newtons 1st Law: Law of Inertia

A

An object in motion tends to stay in motion (in the same direction and at the
same speed), and an object at rest tends to stay at rest, unless acted upon by some net external
force.

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23
Q

Newtons 2nd Law:

A

Fnet = ma
An object of mass will accelerate when the vector sum of the forces result in some nonzero resultant force vector.

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24
Q

Newton’s 3rd Law

A

To every action there is a always an opposed but equal reaction.

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25
Q

Define inertia.

A

An object’s ability to resist changes in its velocity; an object in motion will stay in motion, or an object at rest will stay at rest.

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26
Q

Equation for calculating max static friction

A

Fstatic max = μ x normal force
*μ is a constant which is given

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27
Q

Equation for calculating kinetic friction

A

Fkinetic = μ x normal force
*μ is a constant which is given

28
Q

What is normal force (N)?

A

Normal force is the force that the object exerts on the surface; it’s always perpendicular to the surface.

29
Q

How do you calculate normal force (N) if the surface is horizontal?

A

If the surface is horizontal, N is equal to the magnitude of the weight force.

30
Q

How do you calculate normal force (N) if the surface is inclined?

A

The normal force at an inclined plane = mgcos(inclined angle)

31
Q

True or false:
Kinetic friction only occurs when two surfaces slide against each other.

A

True. A car driving on the road doesn’t have kinetic friction unless it is icy and it starts sliding on the ice.
*Even if an object travels at constant speed, kinetic friction still occurs if two surfaces are sliding against one another.

32
Q

How do you calculate normal force (N) if the surface is vertical?

A

If the surface is vertical, N is equal to the magnitude of whatever force is horizontal on the free body diagram.

33
Q

In a free body diagram of an object, the friction force is always _________ to the surface, while the normal force (N) is ___________ to the surface.

A

tangent (parallel); perpendicular

34
Q

Differentiate avg. acceleration and instantaneous acceleration

A

Average -change in velocity over an amount of time elapsed
Instantaneous - acceleration at a specific point in time

35
Q

What does it mean when you have a positive # velocity and a negative # acceleration:
v = 1 m/s
a = -2 m/s^2

A

It means that even though you are going 1 m/s, you are decelerating (slowing down).

36
Q

Constant acceleration/how graphs look:
Position vs. time graph -
Velocity vs. time graph -
Acceleration vs. time -

A

Position vs. time graph - hyperbola
Velocity vs. time graph - linear
Acceleration vs. time - no slope (horizontal line)

37
Q

What information can you obtain by looking at a position vs. time graph?

A
  1. Positive or negative slope –> direction (right or left) of velocity
  2. Steepness of slope –> not steep = slow velocity; steep = fast velocity
  3. If slope is a hyperbola –> you can tell if the object is moving from slow to fast OR fast to slow depending on the change in steepness of the slope at different points
38
Q

Which graph has a negative acceleration, which one has a positive acceleration?

A

First graph - positive acceleration because object is moving to the right and is speeding up
Second graph - negative acceleration because object is moving to the left and is speeding up

39
Q

If a person is walking to the left and is slow down, their acceleration is (positive/negative).

A

Positive

40
Q

A horizontal line is present on a velocity vs. time graph. What can you infer?

A

The velocity is constant. There is no acceleration.

41
Q

On a graph, the product of the y and x axis is represented as the area under the curve.

A

In this example: area under curve is the velocity.
a*t = ∆v

42
Q

If a ball/object is thrown vertically up, what is the velocity of the object when it reaches its maximum height?

A

Velocity is always 0 at max height.

43
Q

Essential equations for solving a problem under constant acceleration conditions:

A

Helps you find velocity or time it takes to reach max height:
v(final) = v(initial) + at
Helps you find position of object:
y = v(initial)*t + (1/2)at^2
Helps you find the max height:
v^2(final) = v^2(initial) + 2ay

44
Q

What is projectile motion? Give an example?

A

A motion which follows a path along 2 dimensions (horizontal and vertical distances). Example is a cannonball.
*accel. for vertical distance is -10
*accel for horizontal distance is 0

45
Q

Projectile motion: velocity of x and y components

A

Velocity of x component = Vcosθ
Velocity of y component = Vsinθ

46
Q

For an object following projectile motion, there is only acceleration in the vertical direction due to gravity.

A

True, there is no horizontal acceleration.

47
Q

If you have a question including inclined planes (not straight surface), remember these two equations:

A

Weight force in x direction, parallel to surface = mgsin(θ)
Weight force in y direction, perpendicular to surface = mgcos(θ)

48
Q

On an inclined plane, a moving object at constant velocity experiences what kinds of forces?

A

Normal force, weight/gravity on the parallel & perpendicular component, kinetic friction

49
Q

True or false:
An object that begins to slip on the inclined plane: parallel component of weight/gravity > static friction

A

True

50
Q

True or false:
In an object that accelerates down the inclined plane: parallel component of gravity = kinetic friction.

A

False, an object that accelerates down the plane has a greater force of gravity than kinetic friction.

51
Q

What is centripetal force?

A

It is a type of force present in circular motion which always points radially inwards, and keeps the object moving in a circular path.

52
Q

Calculating centripetal force

A

Fc = (mv^2)/r

53
Q

Centripetal acceleration

A

a = v^2/r

54
Q

For circular motion, the acceleration vector is pointing in what direction? And in what direction is the velocity vector pointing?

A

Acceleration always starts from the middle of the moving object towards the center of the circle.
Velocity is always tangential/perpendicular to the acceleration.

55
Q

In uniform circular motion, why is there no work done?

A

There is no work when an object is moving in a circle because the displacement vector and force vector are perpendicular to each other. So cos90 is 0.

56
Q

Calculating gravitational force between two masses

A

Fgravity = (Gm1m2)/d^2
G is a constant: 6.67 x 10^-11

57
Q

How does distance affect gravitational force?
If the distance between two objects doubles, how is the force affected?

A

Fgravity is inversely proportional to radius^2.
As radius increase x2, force decreases x4.

58
Q

Differentiate between static and dynamic equilibrium.

A

Static - when the object is not moving at all
Dynamic - when the object is moving at constant speed (acceleration = 0)

59
Q

Perpendicular = (sin/cos)
Parallel = (sin/cos)

A

Perpendicular = cos
Parallel = sin

60
Q

Define torque

A

Effectiveness of a force to cause an object to rotate about a fixed axis.
Counterclockwise is positive
Clockwise is negative.

61
Q

Formula to calculate torque

A

T = rFsinθ
Counterclockwise: +
Clockwise: -

62
Q
A
63
Q

What is the acceleration for each of the charts?

A

A. Positive acceleration because the velocities are positive numbers and the person is speeding up.
B. Negative acceleration because the velocities are positive, but the person is slowing down.

64
Q

For a free falling object accelerating at constant rate, what is the relationship between time and total distance traveled?

A

Distance is directly proportional to t^2
If t increases x2, d increases x4

65
Q

For a force versus displacement graph, the area under the curve gives you _______.
For a velocity versus time graph the area under the curve gives you ________.
For an acceleration versus time graph, the area under the curve gives you ________.

A

Work
Displacement
Velocity

Malika Physics MCAT (10 decks)

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