Conservation of energy Flashcards – AQA A-level Physics (7408)

What is gravitational potential energy?

Energy associated with an object's position in a gravitational field.

What equation gives the change in gravitational potential energy near Earth's surface, where gravitational field strength is constant?

$\Delta E_p = mg\Delta h$

Here, $m$ is mass, $g$ is gravitational field strength, and $\Delta h$ is the change in height.

How does the sign of the gravitational potential energy change depend on whether an object rises or falls?

Rising gives a positive change; falling gives a negative change.

What height measurement determines the change in gravitational potential energy, regardless of the reference height?

The vertical height difference.

What is kinetic energy?

The energy an object has because of its motion.

What is the formula for the kinetic energy of an object of mass $m$ moving at speed $v$?

$E_k = \frac{1}{2}mv^2$

How does kinetic energy depend on mass and speed?

It is proportional to mass and to the square of speed.

What does the law of conservation of energy state?

Energy cannot be created or destroyed, but it can be transferred between stores or between a system and its surroundings.

How are changes in kinetic and gravitational potential energy related when no energy is transferred by resistance or other processes?

A decrease in one equals the increase in the other.

What happens to mechanical energy when work is done against a resistive force?

It is transferred to other stores, commonly the internal energy of the objects and surroundings.

What is the energy accounting equation when resistance is the only process transferring energy away from kinetic and gravitational potential energy?

$\Delta E_k + \Delta E_p + W_{\text{res}} = 0$ Here $W_{\text{res}}$ is the positive work done against resistance.

What is the work done against a constant resistive force $F$ that directly opposes motion over a distance $d$?

$W_{\text{res}} = Fd$