Energy & Work (OCR A Level Physics): Revision Note

Energy & Work

• Energy is the capacity to do work, therefore:

Transfer of energy = work done

• This principle can be used to form mathematical equations for each type of energy

• The type of transfer of energy depends on the scenario

• The most common types of energy that are transformed between each other are:

Kinetic energy

• Kinetic energy is the work done to accelerate an object from rest to speed v

$E_k=\frac{1}{2}m{v}^2$

• Where:

  • m = mass (kg)

  • v = speed (m s^-1)

Gravitational potential energy

• Gravitational potential energy is the work done against gravity when an object is lifted through a height Δh

$E_p=mg∆h$

• Where:

  • m = mass (kg)

  • g = acceleration due to gravity (m s^-2)

  • Δh = change in height (m)

Elastic potential energy

• Elastic potential energy is the work done in stretching or compressing an object

$E=\frac{1}{2}Fx=\frac{1}{2}k{x}^2$

• Where:

  • F = stretching or compressing force (N)

  • x = extension (or compression) (m)

  • k = force constant (N m^-1)

Thermal

• The energy transferred by heating to change the temperature of a mass m by ΔT is

$E=mc∆T$

• Where:

  • m = mass (kg)

  • c = specific heat capacity (J kg^-1 K^-1)

  • ΔT = change in temperature (K or °C)

Nuclear

• Nuclear energy is released during fission and fusion and is equivalent to the decrease in mass, Δm

$E=∆m{c}^2$

• Where:

  • Δm = mass defect (kg)

  • c = speed of light