KEY EQUATIONS

Question 1

Average speed =

Answer 1

average speed = distance/time

V = d/t

Question 2

Velocity =

Answer 2

Velocity = change in displacement/time taken

Question 3

how to subtract a vector

Answer 3

to subtract a vector, add on the vector to be subtracted in the opposite direction

Question 4

acceleration =

Answer 4

acceleration = gradient of velocity time graph

Question 5

Displacement =

Answer 5

displacement = area under velocity time graph

Question 6

The four equations of motion (Suvat)

Answer 6

V = u + at
S = (u + v)/2 x t
S = ut + 1/2 at²
V² = u² + 2as

Question 7

For a velocity v at an angle θ to the x-direction the components are:

Answer 7

x-direction: v cos θ

y-direction: v sin θ

Question 8

In the absence of air resistance, an object has:

Answer 8

constant velocity horizontally and constant acceleration vertically.

Question 9

Resultant force =

Answer 9

Resultant force = Mass x acceleration

F = ma

Question 10

Weight =

Answer 10

Weight = Mass x acceleration of free fall
W = mg

Question 11

What do all physical quantities have

Answer 11

all physical quantities have a numerical magnitude (a numerical size) and a unit

Question 12

What are base units in mechanics

Answer 12

length, mass, time, current and temperature are base units in mechanics

Question 13

What on each side of a physics equation are the same`

Answer 13

base units on each side of a physics equation are the same

Question 14

What should you do when you draw a scale drawing

Answer 14

when you draw a scale drawing you should:
State the scale used
draw a large diagram to reduce the uncertainty

Question 15

What happens in a body is in equilibrium

Answer 15

if a body is in equilibrium, there is no resultant force and no resultant torque or moment about any point

Question 16

When is work done

Answer 16

work is done on a body when a force moves (displaces) the body in the direction of the force.
Energy is then transferred from one body to another

Question 17

work done =

Answer 17

Work done = force x distance

W = Fs

Question 18

What does work done =

Answer 18

work done = energy transferred

Question 19

Work done (angle)

Answer 19

Work done = Fs Cos θ

Question 20

change in g.p.e =

Answer 20

Change in g.p.e = weight x change in height

ΔEp = mgΔh

Question 21

Kinetic energy =

Answer 21

1/2 x mass x speed²

Ek = 1/2 mv ²

Question 22

Efficiency =

Answer 22

efficiency = useful output energy/total input energy x 100%

Question 23

power =

Answer 23

power = work done/ Time taken 
P = W/t 

OR

Power = force x velocity 
P = F x v

Question 24

Momentum =

Answer 24

Momentum = mass x velocity 
p = mv

Question 25

what happens in a perfectly elastic collision

Answer 25

In a perfectly elastic collision of two bodies the relative speed of the body’s approach is equal to the relative speed of their separation

Question 26

what happens during an inelastic collision

Answer 26

During an inelastic collision the total kinetic energy of the bodies becomes smaller

Question 27

Resultant force is proportional to

Answer 27

Resultant force ∝ rate of change of momentum F = Δp/Δt

Question 28

Density =

Answer 28

density = mass/volume P = m/v

Question 29

pressure =

Answer 29

Pressure = normal force/cross-sectional area P = F/A

Question 30

Change in pressure =

Answer 30

change in pressure = density × acceleration due to gravity × depth Δp= ρgh

Question 31

upthrust =

Answer 31

upthrust = ρgV | = Weight of liquid displaced

Question 32

Spring constant =

Answer 32

spring constant = force/extension | K = F/x

Question 33

strain = extension/original length

Answer 33

strain = extension/original length ε = x/L

Question 34

stress =

Answer 34

Stress = normal force / cross-sectional area σ= F/A

Question 35

charge =

Answer 35

charge = current x time ΔQ = IΔt

Question 36

Energy transferred =

Answer 36

energy transferred = potential difference × charge | ΔW = VΔQ

Question 37

resistance =

Answer 37

resistance = potential difference/current R = v/I

Question 38

Equations for power

Answer 38

Equations for power: P = VI P = I² R P = V²/R

Question 39

resistance =

Answer 39

Resistance = resistivity x length/cross sectional area R = ρL/A

Question 40

Resistivity =

Answer 40

resistivity = resistance x cross-sectional area / length ρ = RA/L

Question 41

Potential difference across a power source =

Answer 41

Potential difference across a power source = | V = E - Ir

Question 42

Intensity =

Answer 42

intensity = power / area

Question 43

What is intensity proportional to

Answer 43

intensity∝amplitude² or I∝A²

Question 44

what does v (wave speed) equal to

Answer 44

v = fλ where v is the speed of the wave, f is the frequency and λ is the wavelength.

Question 45

Doppler effect =

Answer 45

Doppler effect = f0 = fs×v / (v±vs) f0 is the observed frequency Fs is the frequency of the source v is the speed of the wave and vs is the speed of the source relative to the observer

Question 46

Malus’s law:

Answer 46

Malus’s law | I = I0 cos² 0

Question 47

The double slit equation

Answer 47

λ=ax/D λ is the wavelength a is the separation between the centres of the slits X is the separation between the centres of adjacent bright or dark fringers D is the distance between the slits and the screen

Question 48

Determine wavelength λ with a diffraction grating

Answer 48

dsinθ=nλ

Question 49

Wave speed (v) =

Answer 49

v = f λ