Kinetic Energy Flashcards

All 6 cards in this deck

What is the equation for the kinetic energy of a moving object?

$E_k = \frac{1}{2}mv^2$ (kinetic energy = ½ × mass × speed²)

What are the units of each quantity in $E_k = \frac{1}{2}mv^2$?

$E_k$ in joules (J), $m$ in kilograms (kg), $v$ in metres per second (m/s).

What are the steps to calculate kinetic energy?
e.g. a 4 kg ball moving at 3 m/s

1. Square the speed: $3^2 = 9$
2. Multiply by the mass: $4 \times 9 = 36$
3. Halve it: $E_k = 18$ J

What are the steps to find the speed of an object from its kinetic energy?
e.g. $E_k = 100$ J, mass 2 kg

1. Rearrange: $v^2 = \dfrac{2E_k}{m}$
2. Substitute: $v^2 = \dfrac{2 \times 100}{2} = 100$
3. Square root: $v = 10$ m/s

True or false? Doubling the speed of an object doubles its kinetic energy.

False. Kinetic energy depends on speed squared, so doubling the speed gives four times the kinetic energy.

True or false? Doubling the mass of an object at the same speed doubles its kinetic energy.

True. Kinetic energy is directly proportional to mass.