Kinetic, Elastic & Gravitational Potential Energy

Kinetic energy

• The energy in the kinetic store of a moving object (recall this equation):

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

• $E_k$ kinetic energy in joules, J; $m$ mass in kilograms, kg; $v$ speed in metres per second, m/s
• Worked example: a 1200 kg car at 15 m/s. $E_k = 0.5 \times 1200 \times 15^2 = 0.5 \times 1200 \times 225 = 135\,000$ J $= 135$ kJ
• Rearranged for speed: $v = \sqrt{\dfrac{2E_k}{m}}$. Doubling the speed quadruples the kinetic energy