Equations

Question 1

Weight

Answer 1

Weight = mass x gravitational field strength

W = m x g

Question 2

Work done

Answer 2

Work done = force x distance (along the line of action of the force)

(W = F x s)

Question 3

Force applied to a spring

Answer 3

Force applied to a spring = sting constant x extension

F = k x e

Question 4

Moment of a force

Answer 4

Moment of a force = force x distance (normal to direction of force)

M = F x d)

Question 5

Pressure

Answer 5

Pressure = force normal to a surface ÷ area of that surface

p = F ÷ a

Question 6

Distance travelled

Answer 6

Distance travelled = speed x time

s = v x t

Question 7

Acceleration

Answer 7

Acceleration = change in velocity ÷ time taken

a = Δv ÷ t

Question 8

Resultant force

Answer 8

Resultant force = mass x acceleration

F = m x a

Question 9

Momentum

Answer 9

Momentum = mass x velocity

p = m x v

Question 10

Kinetic energy

Answer 10

Kinetic energy = 0.5 x mass x (speed) ²

Ek = 0.5m x v ²

Question 11

Gravitational potential energy

Answer 11

Gravitational potential energy = mass x gravitational field strength x height

(Ep = m x g x h)

Question 12

Power

Answer 12

Power = energy transferred ÷ time

(P = E ÷ t)

OR power = work done ÷ time

(P = W ÷ t)

Question 13

Efficiency

Answer 13

Efficiency = useful output energy transfer ÷ total input energy transfer

OR efficiency = useful power output ÷ total power input

Question 14

Wave speed

Answer 14

Wave speed = frequency x wavelength

v = f x λ

Question 15

Charge flow

Answer 15

Charge flow = current x time

Q = I x t

Question 16

Potential difference (voltage)

Answer 16

Potential difference = current x resistance

V = I x r

Question 17

Power

Answer 17

Power = potential difference x current

(P = V x I)

However p.d. = current x resistance so this can also be written as

Power = (current) ² x resistance

(P = I ² x R)

Question 18

Energy transferred

Answer 18

Energy transferred = power x time

(E = P x t)

OR energy transferred = charge flow x potential difference

(E = Q x v)

Question 19

Density

Answer 19

Density = mass ÷ volume

ρ = m ÷ v

Question 20

Change in internal energy

Answer 20

Change in internal energy = mass x specific heat capacity x temperature change

(E = m x c x ΔT)