Forces & EnergyOxford AQA IGCSE Physics: Flashcards

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Give the equation for work done.

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Give the equation for work done.: W = F x d, where F is force and d is the distance moved in the direction of the force.
What happens to energy when work is done against friction?: Energy is transferred by heating — the object and surroundings warm up.
Give the equation for elastic potential energy.: E_e = 1/2 x k x e^2, where k is the spring constant and e is the extension, valid within the limit of proportionality.
Give the equation for gravitational potential energy.: E_p = m x g x h, where m is mass, g is gravitational field strength, and h is height.
Give the equation for kinetic energy.: E_k = 1/2 x m x v^2, where m is mass and v is speed.
If a car's speed doubles, what happens to its kinetic energy?: It quadruples, because kinetic energy depends on speed squared.
Give the equation for power in terms of energy transferred.: P = E / t, where E is energy transferred and t is time.
Give the equation for power in terms of work done.: P = W / t, where W is work done and t is time.
What is the unit of power?: Watts (W).
A force of 10 N moves an object 5 m in the direction of the force. Calculate the work done.: W = F x d = 10 x 5 = 50 J.
Why does doubling the speed of a car have such a large effect on road safety?: Because kinetic energy increases with the square of speed, so doubling speed quadruples kinetic energy and the energy that must be dissipated to stop.
What is the 'limit of proportionality' in the context of elastic potential energy?: The point up to which extension remains directly proportional to force; beyond it, the elastic potential energy equation no longer applies.