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Physics A-Level AQA > 4 - Mechanics and Materials > Flashcards

4 - Mechanics and Materials Flashcards

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1
Q

What is the difference between a scalar and a vector quantity?

A

A scalar quantity has magnitude only, but a vector has direction and magnitude.

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2
Q

What are some examples of scalar quantities?

A

Length, area, volume, speed, mass, density, pressure, temperature, energy, work, power.

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3
Q

What are some examples of vector quantities?

A

Displacement, velocity, acceleration, momentum, force, lift, drag, thrust, weight.

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4
Q

How should a vector be resolved?

A

Into two components at right angles to each other.

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5
Q

How can the motion of an object be determined from a scale vector addition triangle of the forces acting on it?

A

If the forces form a closed triangle, the object is in equilibrium, but if it is not closed it is accelerating.

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6
Q

What is a free-body diagram?

A

A sketch of an object of interest with all the surrounding objects removed and all of the forces acting on the body shown, allowing for easier visualistion.

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7
Q

If an object has travelled 10m north, then 5m east, what heading is it from its original position?

A

atan(5/10) = 26.6 degrees

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8
Q

If an object is on a slope, how should the forces acting on it generally be resolved?

A

Parallel and perpendicular to the slope.

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9
Q

What is a reaction force?

A
  • Also known as a contact force, normal force, or normal contact force.
  • Related to Newton’s Third Law, if object A exerts a force on object B, object B will exert an equal an opposite force on object A.
  • This “reaction force” is always at a right angle to the point of contact.
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10
Q

With what formulae should the components of a force acting on a slope be resolved?

A

W = Weight (N), θ = Slope angle
Component parallel to the slope = Wsin(θ)
Component perpendicular to the slope = Wcos(θ)

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11
Q

How is the moment of a force calculated?

A

F = Force (N), d = perpendicular distance from the pivot to the line of action of the force (m)
Moment of a force (Nm) = Fd

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12
Q

What is the definition of the centre of mass of a body?

A

The point through which a single force of the body has no turning effect.

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13
Q

What are unstable and stable equilibria?

A

A stable equilibrium is one where if a body is disturbed, it tends to return to its original position.
An unstable equilibrium is where upon being disturbed, the body tends to keep moving away from the original position.

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14
Q

What causes a body to topple?

A

The body topples when the centre of mass is no longer above the base of the object. The line of action of the body’s weight acts any further than directly through the pivot.

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15
Q

What is a couple?

A

A couple is a pair of equal and opposite forces acting on a body, but not along the same line - they have a perpendicular distance between them.

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16
Q

What is the moment of a couple?

A

F - Force (N), d - perpendicular distance between the lines of action of the forces (m)
Combined moment of the couple (Nm) = Fd

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17
Q

Where is the centre of mass of a uniform regular solid?

A

At its centre.

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18
Q

What is the definition of displacement?

A

Distance moved from the starting point, with direction. (s)

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19
Q

What is the definition of initial velocity?

A

Velocity at the start. (u)

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20
Q

What is the definition of final velocity?

A

Velocity at the end. (v)

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21
Q

What is the definition of acceleration?

A

Rate of change of velocity. (a)

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22
Q

What is the definition of time.

A

I don’t know I just work here. (t)

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23
Q

How is velocity calculated?

A

s - Displacement (m), t - Time (s)
v (ms-1) = Δs/Δt

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24
Q

How is acceleration calculated?

A

v - Velocity (ms-1), t - Time (s)
a (ms-2) = Δv/Δt

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25
Q

What is the significance of the area under a velocity-time graph?

A

It is equal to the distance travelled.

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26
Q

What is the significance of the gradient of a displacement-time graph?

A

It is equal to the velocity.

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27
Q

What is the significance of the gradient of a velocity-time graph?

A

It is equal to the acceleration.

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28
Q

What is the significance of the area under an acceleration-time graph?

A

It is equal to the total change in velocity during the journey.

29
Q

What is the suvat equation linking u, v, a, and t?

A

v = u + at

30
Q

What is the suvat equation linking s, v, a, and t?

A

s = vt - 0.5(at^2)

31
Q

What is the suvat equation liking s, u, a, and t?

A

s = ut + 0.5(at^2)

32
Q

What is the suvat equation linking s, u, v, and t?

A

s = 0.5t(u + v)

33
Q

What is the suvat equation linking u, v, a, an t

A

v^2 = u^2 + 2as

34
Q

What is acceleration due to gravity? (g)

A

9.81ms-2

35
Q

What are the good starting steps for solving a suvat calculation?

A
  • Decide which directions will be positive and negative in the x-/y- planes.
  • If an object is in free-fall, acceleration (a) will be 9.81 or -9.81 depending on the previous point.
  • If an object starts from rest, u = 0
  • If a projectile is launched and there is no air resistance, ux = vx
  • The time in both the x-/y- plane is the same, which can be useful.
  • Write down the quantities you have, and the quantity you need to work out, then decide the correct suvat equation to use with them.
36
Q

What is a light gate?

A

A piece of equipment that measures the velocity of an object at two points.

37
Q

You are given the launch angle and velocity of a projectile. What should the first step be?

A

Resolving the initial vector into its two components in the x-/y- planes.

38
Q

What is terminal speed/velocity?

A

The speed at which the weight force is equal to the drag force in the opposite direction, and resultant force and acceleration is zero.

39
Q

What is a force?

A
  • A push or pull on an object
  • Forces are vectors with magnitude and direction
  • Forces cause an object to accelerate
40
Q

What is the definition of Newton’s First Law?

A

A body will continue in a state of rest or uniform motion in a straight line unless acted upon by an unbalanced force, also known as the Law of Inertia.

41
Q

What are the implications of Newton’s First Law?

A

If there is zero resultant force on a body, it cannot accelerate, so will move at constant velocity - it cannot turn, speed up, or slow down.

42
Q

What is inertia?

A

The ability of a body to resist acceleration by a net force.

43
Q

What is the equation of Newton’s Second Law?

A

F - force (N), m - mass (kg), a - acceleration (ms-2)
∑F = ma
One newton is the force required to accelerate a mass of 1kg at a rate of 1ms-2
This is applicable only when mass is constant.

44
Q

What is the equation linking weight, mass, and gravity?

A

W - weight (N), m - mass (kg), g - gravitational field strength
W = mg

45
Q

What is apparent weight?

A
  • If an object subject to gravity is not in free fall, then there is a reaction force acting in opposition to gravity.
  • This reaction force is sometimes referred to as apparent weight.
  • In an elevator, your apparent weight increases when you are accelerating upwards, and decreases when accelerating downwards, but is equal to your weight when you are moving at constant velocity.
46
Q

What are the five requirements of a Newton’s Third Law pair?

A
  1. A pair of forces
  2. Equal in magnitude
  3. Opposite in direction
  4. Of the same type
  5. Acting on different bodies
47
Q

What is the definition of energy?

A

The stored ability to do work.

48
Q

What is the definition of work?

A
  • Defined by the equation:
    work = force x distance moved in the direction of the force
    W - work done (J), F - force (N), s - displacement (m), θ - angle to direction of movement
    W = Fscos(θ)
  • Work is a scalar quantity, not a vector - this definition is misleading but correct.
49
Q

What is the work done if a weight of 40N is raised by a height of 5m?

A

W = fs
40 x 5 = 200
200J of work done

50
Q

What is the definition of a joule?

A

One joule is the work done when a force of one newton moves its point of application one metre in the direction of the force.

51
Q

What is the definition of, and equation for, kinetic energy?

A

Kinetic energy is the work an object can do by virtue of its speed.
Ek - kinetic energy (J), m - mass (kg), v - velocity (ms-1)
Ek = 0.5mv^2

52
Q

What is the definition of, and equation for, gravitational potential energy?

A

Gravitational potential energy is the energy stored in an object (the work an object can do) by virtue of its position in a gravitational field.
Ep - gravitational potential energy (J), m - mass (kg), g - gravitational field strength (Nkg-1), h - height (m)
Ep = mgh

53
Q

What is the definition of, and equation for, power?

A

Power is the rate at which work is done.
P - power (W), W - work done (J), t - time (s)
P = W/Δt
or
P - power (W), F - force (N), v - velocity/speed (ms-1)
P = Fv

54
Q

What is the equation for efficiency?

A

Efficiency = useful energy out/total energy in
Percentage efficiency = 100 x useful energy out/total energy in

55
Q

What is air resistance?

A

Air resistance is a type of drag - a friction force opposing the motion of an object travelling through air. It increases with speed.

56
Q

What is the effect of air resistance on a projectile, compared to a projectile launched in the same manner without air resistance present?

A

The trajectory of the object with air resistance will have:
* A lower maximum height
* A non-symmetrical trajectory
* Will travel less far horizontally, if both have horizontal velocity

57
Q

What factors affect the maximum speed of a vehicle?

A
  • Its engine power
  • Its aerodynamicity or drag
  • The surface it is travelling on, namely its friction
58
Q

What is the principle of moments?

A

When a body is in rotational equilibrium, the total clockwise moments are equal to the total anticlockwise moments about the same point.

59
Q

What is the definition of, and equation for, momentum?

A

P - momentum (kgms-1), m - mass (kg), v - velocity (ms-1)
P = mv

60
Q

What is the principle of conservation of linear momentum?

A

When two objects collide in an isolated system, the total momentum before and after the collision remains equal.

61
Q

How are the rate of change of momentum and force related?

A

Force is the same as the rate of change of momentum:
F - Force (N), m - mass (kg), v - speed (ms-1), mv = p = momentum (kgms-1), t - time (s)
F = Δ(mv)/Δs

62
Q

What is an elastic collision?

A

A collision where kinetic energy is conserved, as well as momentum. This is typically when the first object is moving, collides, then stops still, transferring all of its energy to the other object.

63
Q

What is an inelastic collision?

A

A collision where kinetic energy is not conserved. This means kinetic energy has been transformed into something else, like heat or sound.

64
Q

What is a perfectly inelastic collision?

A

A collision where the minimum amount of kinetic energy is conserved - the objects join together and travel at the same velocity afterwards.

65
Q

What is impulse?

A

The force applied over the time of impact of a collision.
Impulse is equal to the change in momentum, so the units of Ns and kgms-1 are equal.
FΔt = mΔv

66
Q

What is the significance of the area under a force-time graph?

A

It is equal to the change in momentum, in Ns, and therefore in kgms-1 also given that the units are equivalent.

67
Q

Why are explosions significant in terms of change of momentum?

A

The total momentum of the exploded object (the parts it breaks into) will be zero.

68
Q

What is the principle of the conservation of energy?

A

Energy is neither created nor destroyed, but may transform from one type to another by doing work against a resistive force.

Physics A-Level AQA (4 decks)

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