Energy stores, transfers and conservation

Which statement best describes the conservation of energy?

The total energy of a closed system remains constant

A moving car has energy mainly in which store?

Kinetic store

Which energy store increases when an object is raised above the ground?

Gravitational potential store

What is meant by transferring energy mechanically?

Energy is transferred by a force moving through a distance

Energy transferred by an electric current follows which pathway?

Electrically

When a hot object warms a cooler object in contact with it, energy is transferred mainly by which pathway?

Heating

Which equation gives the kinetic energy of an object of mass m moving at speed v?

Ek = ½mv²

What happens to an object's kinetic energy if its speed doubles while its mass stays constant?

It becomes four times as large

Near Earth's surface, which equation gives the change in gravitational potential energy when a mass is raised through height h?

ΔE = mgh

A stretched spring stores energy in which store?

Elastic potential store

For a spring obeying Hooke's law, which equation gives its elastic potential energy?

Ee = ½ke²

What is the internal energy of a system?

The total kinetic and potential energies of its particles

During braking, where is much of a vehicle's kinetic energy transferred?

To the thermal stores of the brakes and surroundings

What does it mean when energy is described as dissipated?

It has been transferred to less useful stores, often in the surroundings

Which expression calculates the efficiency of an energy transfer?

Useful energy output divided by total energy input

An appliance receives 500 J of energy and transfers 400 J usefully. What is its efficiency?

80%

What does power measure?

The rate at which energy is transferred

Which statement about energy transfer diagrams is correct?

The total energy entering must equal the total energy leaving