Mechanics

Question 1

Scalars

Answer 1

quantities that only have a magnitude

Question 2

Vectors

Answer 2

quantities that have both direction and magnitude

Question 3

Distance

Answer 3

how far you have travelled

Question 4

Displacement

Answer 4

is the distance travelled in a particular direction

Question 5

Speed

Answer 5

is the rate of change of distance (distance/time)

Question 6

Velocity

Answer 6

is the rate of change of displacement (displacement/time)

Question 7

Instantaneous Speed

Answer 7

means the rate of change of distance at one particular time

Question 8

Average Speed

Answer 8

means the speed over a period of time

Question 9

Acceleration

Answer 9

is the rate of change of velocity (change in velocity/time)

Question 10

Displacement - time graphs

Answer 10

gradient = velocity

Question 11

Velocity - time graphs

Answer 11

gradient = acceleration
area below the line = displacement

Question 12

Acceleration - time graphs

Answer 12

area below the line = change in velocity

Question 13

Projectile Motion

Answer 13

a projectile is an object moving through the air under the influence of only one force (gravity). The trajectory it will follow is a parabola as:
- the VERTICAL component of velocity is constantly changing (due to gravity)
the HORIZONTAL component of the velocity is constant (assuming no air resistance)

Question 14

How does projectile motion differ in reality with air resistance?

Answer 14

• the range is shorter
• the maximum height is lower and is reached earlier
• the gradient is steeper on the way down

Question 15

Projectiles that are launched horizontally

Answer 15

initial vertical velocity = zero
horizontal velocity = launch velocity, v

Question 16

Projectiles that are launched above the horizontal

Answer 16

initial vertical velocity = v sinθ
horizontal velocity = v cosθ

Question 17

Projectiles that are launched at an angle below the horizontal

Answer 17

initial vertical velocity = v sinθ
horizontal velocity = v cosθ

Question 18

5 Key Points of Projectile Motion

Answer 18

• at the highest point, velocity = 0
• acceleration is always downwards at 9.81 ms-2
• horizontal velocity is zero
• range = horizontal velocity x time of flight
• problems may be solved using kinematic equations or conservation of energy

Question 19

What does the Magnitude of Fluid Resistance (drag) depend on?

Answer 19

• the velocity of the object relative to the fluid
• the size and shape of the object
• the fluid used (its viscosity)
• fluids are either liquids or gases

Question 19

What is terminal velocity?

Answer 19

when an object falls under the influence of gravity, it will initially accelerate at 9.81 ms-2
however, the magnitude of air resistance increases as the objects velocity increases
so it will continue to accelerate but less than 9.81 ms-2
once the magnitude of the upwards air resistance = downwards gravitational force, the object will no longer accelerate, as forces are balanced and it is at terminal velocity

Question 20

Mass (m)

Answer 20

is the amount of matter in an object. It is measured in kg and does not change with a change in position

Question 21

Weight (W)

Answer 21

is the force of gravity acting on an object. It is measured in newtons (N). It will change if an object changes its position.
* always is straight down

Question 22

Normal Reaction Force

Answer 22

when an object pushes down on a surface, the surface pushes back on the object. The normal reaction force is always perpendicular to the surface the object is on.

Question 23

Balanced Forces

Answer 23

the object will remain at rest or will continue to move in a straight line at a constant speed

Question 24

Unbalanced Forces

Answer 24

the object will accelerate in the direction of the net force

Question 25

Newtown’s First Law

Answer 25

“an object continues in uniform motion in a straight line or at rest unless a resultant external force acts.”
*if resultant force = zero, object is said to be at translational equilibrium

Question 26

Newton’s Second Law

Answer 26

“the resultant force on an object is proportional to the acceleration providing the mass of the object remains constant.”

Question 27

Newton’s Third Law

Answer 27

“for every action on one object there is an equal but opposite reaction on another object.”
i.e. forces come in pairs (and will be of the same type)

Question 28

Resolving forces

Answer 28

resolving means to break down a force into two components
the components can be found in a number of ways including pythagorus, trigonometry or scale diagrams

Question 29

Resultant Forces

Answer 29

a resultant force is the sum of all the forces acting on an object

Question 30

Resolving Forces of an object on an incline

Answer 30

the weight force can be resolved into two forces:
- parallel to the slope (mg sinθ), this will = friction if speed is constant
- perpendicular to the slope (mg cosθ), = normal reaction

Question 31

Solid Friction (Ff)

Answer 31

is the force that opposes the relative motion of the surfaces of two solid objects.
two types:
- static friction: occurs when there is no relative motion between the surfaces. A force is applied to an object resting on a surface, but the force is not large enough to move the object.
- dynamic friction: occurs when there is relative motion between the surface. Once the force applied to the object exceeds the maximum value of static friction force the object will begin to slide. The magnitude of the dynamic friction force is less than the maximum static value and is a constant.

Question 32

Definition of Energy

Answer 32

it is the “capacity to do work”

Question 33

Kinetic Energy

Answer 33

is the energy an object has because it is moving

Question 34

Gravitational Potential Energy

Answer 34

the energy an object has because of its height above the ground

Question 35

Elastic Potential Energy

Answer 35

this is the energy stored when an object is either stretched or compresses

Question 36

Hooke’s Law

Answer 36

the extension of a spring is proportional to the applied force
F = k x change in X
X = extension or compression (m)
K = spring constant (Nm-1)

Question 37

Law of Conservation of Energy

Answer 37

energy can be converted from one type to another. It cannot be created or destroyed.

Question 38

Work

Answer 38

is said to be done when a force moves an object through a displacement
therefore it is a transfer of energy

Question 39

Power

Answer 39

is the rate at which work is done or energy is transferred

Question 40

Linear Momentum (p)

Answer 40

is defined as the product of mass and velocity. It is a vector

Question 41

Law of Conservation of Momentum

Answer 41

the total linear momentum of a system remains constant provided no resultant external force acts
* therefore total pbfore = total pafter

Question 42

Elastic Collsion

Answer 42

no kinetic energy is lost during the collision (in reality, only occurs between sub-atomic particles)

Question 43

Inelastic Collision

Answer 43

kinetic energy is lost (converted to heat and sound)
however, total amount of energy still remains constant

Question 44

Impulse

Answer 44

is the change in momentum

Question 45

Explosions

Answer 45

typically a stationary system will break apart into two pieces. As with collisions the total momentum is conserved and will be equal to zero.