Kinetic Energy Flashcards

All 7 cards in this deck

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

$KE = \frac{1}{2} \times m \times v^2$ (kinetic energy in J, mass in kg, speed in m/s)

What are the steps to calculate the kinetic energy of a moving object?

e.g. mass $4$ kg moving at $3$ m/s

1. Write the equation: $KE = \frac{1}{2} \times m \times v^2$
2. Substitute: $\frac{1}{2} \times 4 \times 3^2$
3. Evaluate: $18$ J

What are the steps to find the speed of an object from its kinetic energy?

e.g. $KE = 100$ J, mass $8$ kg

1. Write the equation: $KE = \frac{1}{2} \times m \times v^2$
2. Rearrange: $v = \sqrt{\dfrac{2 \times KE}{m}} = \sqrt{\dfrac{2 \times 100}{8}}$
3. Evaluate: $5$ m/s

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

False. Kinetic energy is proportional to (speed)$^2$, so doubling the speed makes the kinetic energy four times larger.

How many joules are there in $1$ kJ?

$1000$ J.

What shape is a graph of kinetic energy against speed for a fixed mass?

An upward curve through the origin (getting steeper), because $KE \propto v^2$ — not a straight line.

True or false? On a graph of kinetic energy against speed for a fixed mass, the kinetic energy read off at $20$ m/s is four times the value read off at $10$ m/s.

True. Kinetic energy is proportional to (speed)$^2$, so tripling the speed instead would give nine times the energy.