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A-Level Physics [Edexcel] > Mechanics > Flashcards

Mechanics Flashcards

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1
Q

What are scalar quantities?

A

Scalar quantities have magnitude only.

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2
Q

What are vector quantities?

A

Vector quantities have a magnitude and a direction.

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3
Q

Scalar or Vector?

  1. Distance
  2. Mass
  3. Velocity
  4. Energy
  5. Weight
  6. Acceleration
  7. Temperature
  8. Displacement
  9. Force
  10. Speed
A
  1. Scalar
  2. Scalar
  3. Vector
  4. Scalar
  5. Vector
  6. Vector
  7. Scalar
  8. Vector
  9. Vector
  10. Scalar
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4
Q

What should an appropriate scale look like?

A

An appropriate scale should maximise the amount of graph space available.

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5
Q

Calculating the final vector can be done in two ways:

A
  • By measurement of the diagram, if it is drawn to scale

- By using Pythagoras/trigonometry

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6
Q

How would you work out the magnitude of a vector?

[Use the following question as an example]

A 3N northwards force and a 4N eastwards force act on a mass. What is the magnitude of the resultant force?

A

√3² + 4²
=√9 + 16
=√25
=5N

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7
Q

How would you work out the direction of a vector?

[Use the following question as an example]

A 3.0N northwards force and then a 4.0N eastwards force act on a mass. What is the direction of the resultant force?

A
  • Draw Triangle.
    (AB=3, BC=4)
  • Lable angle required.
    (BAC)
  • Lable sides of the triangle with opposite-adjacent-hypotenuse.
  • Choose the correct equation from SohCahToa.
    (In this case Toa)
  • Write out the formula with know values.
    (Tan(θ) = 4/3)
  • Rearrange and solve, giving the answer to an appropriate s.f
    (Tan⁻¹(4/3) = θ, θ = 53⁰)
  • Write the answer in relation to the direction.
    (53⁰ East from North/the verticle)
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8
Q

How would you resolve a vector?

A
  • Sketch the vector.
  • Lable sides of the triangle with opposite-adjacent-hypotenuse.
  • Choose the correct equation from SohCahToa.
  • Write out the formula with know values.
  • Rearrange and solve, giving the answer to an appropriate s.f
  • Repeat the same steps for the other axis.
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9
Q

What are the suvat quantities?

A

s: distance
u: initial velocity
v: final velocity
a: acceleration
t: time

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10
Q

What is instantaneous velocity?

A

Velocity at a given point

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11
Q

What is average velocity?

A

Can be found using (u + v)/2

if acceleration is constant

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12
Q

What is rectilinear motion?

A

Moving in a straight line.

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13
Q

What is the vertical acceleration due to gravity?

A

9.81ms⁻²

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14
Q

Displacement-time graphs:

What does the gradient show?

A

Velocity (not speed because a direction is shown)

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15
Q

Velocity-time graphs:

What does the gradient show?

What does the area under the graph show?

A

Gradient: Acceleration.

Area: Displacement.

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16
Q

What is newtons first law?

A

An object at rest will remain at rest…
An object in motion will remain in motion…

…unless acted on by an unbalenced force.

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17
Q

What is newtons second law?

A

The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.

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18
Q

What is newtons second law?

quantativly

A

∑F = ma

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19
Q

What is newtons third law?

A

Every action has an equal but opposite reaction.

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20
Q

Is momentum scalar or vector?

A

Vector.

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21
Q

How do you calculate momentum (p) given the mass and velocity of an object.

A

p = mv

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22
Q

What is the law of conservation of momentum?

A

The total momentum before must be the same as the total momentum after, because linear momentum is always conserved (provided no external force acts on the bodies).

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23
Q

How do you quantitivly show conserved momentum when the masses move off together?

A

mₜ₁vₜ₁ + mₜ₂ vₜ₂ = (mₜ₁ + mₜ₂) vₜ₁₂

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24
Q

How do you quantitivly show conserved momentum when the masses move off separately?

A

mₜ₁vₜ₁ + mₜ₂ vₜ₂ = mₜ₁vₛ₁ + mₜ₂ vₛ₂

25
Q

Using newton’s second law, derive the equation of resultant force.

A

F=ma

Using Newton’s 2nd law:
a= Δv / Δt

∴
F=mΔv / Δt

or as…
F= Δ(mv) / Δt

∴ resultant force = change itn momentum / time interval

26
Q

What is impulse?

A

Where the change in momentum is equal to the resultant force multiplied by time

27
Q

What is impulse?

quantitivly

A

F= Δ(mv) / Δt

or as…

FΔt = Δmv

28
Q

When is the impulse on two objects the same?

A

When two objects move apart in opposite directions the force on each must be the same (2nd law) and the time must also be the same.

29
Q

What is the unit for impulse?

A

Ns

Newton seconds

30
Q

What is the moment?

A

The turning effect of a force.

31
Q

What factors effect moments?

A

The moment of a given force depends on…

…The size of the force.

…The perpendicular distance between the line of the force and the axis of rotation.

32
Q

Relate moments to the force exerted.

A

moment of force = Fx

33
Q

State the principle of moments.

A

The sum of the clockwise moments must be equal to the sum of anticlockwise moments if an object is in equilibrium (not accelerating).

34
Q

Quantitivly show the principle of moments.

A

F₁x₁ = F₂x₂

35
Q

Cranes lift heavy building materials using a horizontal arm called a jib. A hook moves up and down the jib and can lift loads from different points. Cranes have a counterweight balanced at the other end of the jib.
Use your understanding of moments to explain why cranes need to have a counterbalance. Why is it useful to be able to lift loads from different points on the jib?

A
  • Without the counterweight, the crane would topple over.
  • The counter-weight creates a moment that opposes the moment from the load.
  • In order to balance the crane, you need to make the clockwise moment, and anticlockwise moment, equal.
  • Heavier masses can be lifted closer to the pivot in order to equal the moment of smaller masses lifted further away from the pivot.
  • This will ensure that the clockwise and anticlockwise moments are equal.
36
Q

What is a couple?

A
  • When you apply two moments to an object.

- For example when turning a tap.

37
Q

What is torque?

A

The overall turning effect.

38
Q

How do you calculate torque?

A

clockwise torque = Σclockwise forces.

anticlockwise torque = Σanticlockwise forces.

39
Q

Define kinetic energy.

A

The ability of an object to do work due to its motion.

40
Q

Define gravitational potential energy.

A

The potential that an object has due to it being elevated in a gravitational field.

41
Q

Define work done.

A

Where energy is transferred to or from an object.

42
Q

Define power.

A

The energy transferred per unit time.

43
Q

Define the law of conservation of energy.

A

Energy can never be created or destroyed. It can only be transferred from one store or location to another.

44
Q

Define efficiency.

A

The ratio of useful energy transferred to total energy supplied.

45
Q

Define a joule.

A

The standard unit for one Newton metre.

46
Q

Quantitivly show workdone in relation to a change in distance.

A

ΔW = FΔs

47
Q

When does an object have potential energy?

A

When an object is able to do work due to its position or state.

48
Q

Quantitivly show:

The increase in GPE is equal to the work done to lift the object to a height, h.

The increase in EPE is equal to the work done to stretch the object by an extension, x.

A

W = mgΔh

W = FₐᵥΔx

49
Q

What does a distance-time graph describe?

A

The journeys of different objects.

50
Q

What does a velocity-time graph describe?

A

The speed of an object changes.

51
Q

What does a flat horizontle line show in a distance-time graph?

A

When an object is stationary.

52
Q

What does a flat horizontle line show in a velocity-time graph?

A

Constant speed.

53
Q

What does a steep, diagonal line show in a distance-time graph?

A

When an object is travelling quickly.

54
Q

What does a steep, diagonal line show in a velocity-time graph?

A

Constant acceleration.

55
Q

What do lines moving away from the x-axis in a distance-time graph show?

A

Moving away from the starting point.

56
Q

What do lines moving towards the x-axis in a displacement-time graph show?

A

Moving towards from the starting point.

57
Q

What do lines moving towards the x-axis in a velocity-time graph show?

A

Slowing down.

58
Q

What do lines moving below the x-axis in a velocity-time graph show?

A

Changing direction.

59
Q

What does the area under the graph show in a velocity-time graph?

A

Distance travelled.

A-Level Physics [Edexcel] (9 decks)

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