Formulas and units

Question 1

speed equation

Answer 1

v= s/t (speed= displacement/time)

Question 2

average speed equation

Answer 2

average speed= total distance travelled/total time taken

Question 3

acceleration equation

Answer 3

a= ∆v/∆t (acceleration= final velocity - initial velocity/ change in time)

Question 4

weight equation

Answer 4

W=mg (weight= mass x gravitational field strength)

Question 5

force equation

Answer 5

F=ma (Force= mass x acceleration)

Question 6

density equation

Answer 6

ρ = m/V (density= mass/volume)

Question 7

pressure formula

Answer 7

P=F/A (pressure= force/area)

Question 8

fluid pressure formula

Answer 8

P=ρgh (pressure= density x gravitational field strength x height/depth)

Question 9

spring constant equation

Answer 9

k = F/x (spring constant= force/extension)

Question 10

moment formula

Answer 10

moment = force × perpendicular distance from the pivot

Question 11

momentum formula

Answer 11

p= mv (momentum = mass x velocity)

Question 12

impulse formula

Answer 12

impulse = force x time for which force acts
impulse = F∆t = ∆(mv)

Question 13

force formula

Answer 13

F = ∆p/∆t

Question 14

work equation

Answer 14

W= Fd (work= force x parallel distance

Question 15

kinetic energy equation

Answer 15

Ek= 1/2mv^2 (kinetic energy= 1/2 x mass x velocity^2)

Question 16

gravitational potential energy equation

Answer 16

∆Ep = mg∆h (gravitational potential energy = mass x gravitational field strength x height)

Question 17

What is work equal to?

Answer 17

∆E (change in kinetic energy)

Question 18

Power equation (mechanical)

Answer 18

P=W/t (power= work/time)
also P=∆E/t

Question 19

Power equation (electric)

Answer 19

P=VI (power= voltage x current)

Question 20

percentage efficiency equation

Answer 20

(%) efficiency = (useful energy output)/(total energy input) (× 100%)
(%) efficiency = (useful power output)/ (total power input) (× 100%)

Question 21

Temperature in kelvin equation

Answer 21

T (in K) = θ (in °C) + 273

Question 22

Equation for fixed mass of gas at constant temp

Answer 22

pV = constant

Question 23

heat capacity equation

Answer 23

c = ∆E/m∆θ

Question 24

wave speed equation

Answer 24

v = fλ

Question 25

energy (latent heat) equation

Answer 25

e=mL (energy = mass x specific latent heat)

Question 26

pressure and volume temperature equation

Answer 26

pV=nRT (pressure x volume = moles x gas constant x temperature in kelvin)

Question 27

refractive index equations

Answer 27

n = sin(i)/sin(r)
n = 1/sin(c)
Refractive index (n) = speed of light in vacuum or air (c)/speed of light in medium (V)

Question 28

frequency equation

Answer 28

f= 1/T
(frequency = 1/period)

Question 29

charge equation

Answer 29

Q=It (charge = current x time)

Question 30

potential difference and electromotive force equation

Answer 30

E or V= W/Q (emf or pd = work done/ charge quantity)

Question 31

electric energy equation

Answer 31

E=VIt (power x time)

Question 32

resistance equation

Answer 32

R=V/I (voltage/resistance)

Question 33

equation for potential divider

Answer 33

R1/R2=V1/V2 (resistance 1/resistance 2 = voltage 1/voltage 2)

Question 34

power in wires equation

Answer 34

P=I^2R (power= current^2 x resistance)

Question 35

Equation for 100% efficiency transformer

Answer 35

I(p)V(p)=I(s)V(s)
current (primary) x potential difference (primary) = current (secondary) x potential difference (secondary)

Question 36

Transformer equation

Answer 36

V(p)/V(s) = N(p)/N(s)
(potential difference primary/ potential difference secondary = number of turns primary/ number of turns secondary)

Question 37

orbital speed equation

Answer 37

v = 2πr/T (speed= 2 x pi x average radius of orbit/ orbital period)

Question 38

Hubble constant equation

Answer 38

H0=v/d (Hubble constant= speed at which galaxy is moving away from the earth/ distance from the earth)

Question 39

age of universe equation

Answer 39

1/H0= d/v

Question 40

Current estimate for hubble constant

Answer 40

2.2 × 10^–18 per second