10.4 Energy and efficiency

Question 1

How can work done be calculated

Answer 1

W=Fs

Question 2

If an object moves at a constant velocity, due to the force being opposed by an equal and opposite force caused by friction, a distance of s=vt is moved.

Therefore:

Answer 2

Output power Pout=Fv

Question 3

What is useful energy

Answer 3

Energy transferred for a purpose

Question 4

Efficiency equation

Answer 4

Efficiency=useful energy transferred by the machine/energy supplied to the machine = work done by the machine/energy supplied to the machine

Question 5

How can efficiency be expressed

Answer 5

The output power of a machine/the input power to the machine

Question 6

Calculate percentage efficiency

Answer 6

% efficiency = efficiency * 100

Question 7

Can energy being wasted always be stopped?

Answer 7

No. Eg. Car engines would overheat if they were insulated

Question 8

The kinetic energy of a mass m of wind moving at speed v=1/2ρv^2

SO kinetic energy per second of wind passing through a wind turbine:

Answer 8

1/2ρv^2vA=1/2ρv^3A

Question 9

What is the density of air

Answer 9

1.2kgm^-3

Question 10

In a British summer, how much solar energy can a solar heating panel absorb

Answer 10

500 Js^-1

Question 11

The UK energy demand uses about ___% of out total energy supply

Answer 11

30%