Numford

MechanicsClass 11, Work, Energy and Power

Dimensional formula of Potential energy

[M L2 T-2]

SymbolU SI unitjoule (J)

Stored energy, mgh near the Earth. It has the dimension of work.

Derivation

How to get the dimensional formula of potential energy

  1. Start from the definition: potential energy = mass × acceleration due to gravity × length.
  2. velocity = length / time, so velocity is [L] / [T] = [L T-1].
  3. acceleration = velocity / time, so acceleration is [L T-1] / [T] = [L T-2].
  4. force = mass × acceleration, so force is [M] × [L T-2] = [M L T-2].
  5. gravitational constant = force × length2 / mass2, so gravitational constant is [M L T-2] × [L]2 / [M]2 = [M-1 L3 T-2].
  6. acceleration due to gravity = gravitational constant × mass / length2, so acceleration due to gravity is [M-1 L3 T-2] × [M] / [L]2 = [L T-2].
  7. Put in the dimension of each part: [M] × [L T-2] × [L].
  8. Add the powers of each base quantity: [M L2 T-2].
Same dimensions

Quantities with the dimensions [M L² T⁻²]

Equal dimensions do not make them the same quantity. Compare potential energy with the others in the full grid.

Practice

Three questions on potential energy

1Which of these has the same dimensions as potential energy?

2What is the SI unit of potential energy?

3Which one has different dimensions from the others?

Questions

Potential energy: quick answers

What is the dimensional formula of potential energy?

The dimensional formula of potential energy is [M L² T⁻²]. It comes from potential energy = mass × acceleration due to gravity × length.

What is the SI unit of potential energy?

The SI unit of potential energy is the joule (J).

Which quantities have the same dimensions as potential energy?

Potential energy shares [M L² T⁻²] with work, energy, kinetic energy, torque, torsional constant, gravitational potential energy, strain energy, heat. Equal dimensions do not make them the same quantity.

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