Formulas & tables/Physics/Work, energy, power/Kinetic energy

Kinetic energy

Ek=12mv2E_k=\tfrac12 m v^2

Result unit: J (joule)

What it describes

The energy a body has because of its motion.

Symbols

EkE_k
kinetic energy
[J]
mm
mass
[kg]
vv
speed
[m/s]

Where it comes from

The energy of motion grows with the square of the speed — a car moving twice as fast has four times the kinetic energy (and braking distance). The change in EkE_k equals the work done by the net force.

When to use it

Bodies in motion, collisions, braking. Work–energy theorem: W=ΔEkW=\Delta E_k.

Example

A body of mass 2 kg moves at 10 m/s. Find its kinetic energy.
Substitutionm=2m=2 kg, v=10v=10 m/s.
ResultEk=12⋅2⋅102=100E_k=\tfrac12\cdot2\cdot10^2=100 J.

Related formulas

Mechanical work Conservation of mechanical energy

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