# Energy efficiency

```Energy efficiency questions
L
1. A roller coaster at the top of the ride is a gravitational potential energy store. As it goes
down the track its kinetic energy store increases (a useful energy transfer), and the
gravitational potential store empties.
Which stores of energy are increased due to wasted energy transfers? [2 marks] [grade 2]
2. A ball storing 10 J of gravitational potential energy is dropped to the floor. After bouncing
back up, the ball’s store of gravitational potential energy at its highest point has reduced
to 7 J.
a. How much energy has been wastefully transferred as the ball bounced? [1]
b. What is the efficiency of the ball as it bounces?
[2]
3. A kettle transfers 1,500 J of energy, 1,200 J to a thermal energy store in the water and
300 J to the air as sound. How efficient is the kettle?
4. Playing on an Xbox 360 transfers 102 J of energy each second. 9 J of this energy is
transferred to a thermal energy store. How efficient is the Xbox?
[2]
5. A pendulum with a store of 100 J of gravitational potential energy transfers 99.5J to a
kinetic energy store on its first swing.
a. How much energy is being wasted due to friction by transfer to a thermal energy
store?
[1]
b. How efficient is the pendulum?
[2]
6. What is the energy efficiency of a car that transfers 15 kJ of the chemical energy stored in
its petrol into 3,000 J of kinetic energy stored in its movement?
7. An iPod transfers 4 J of from a chemical energy store each second. 3.5 J is transferred to
a magnetic energy store (the memory storage), which in turn transfers 3.25 J by sound and
light radiation. The rest of the energy is wasted as thermal energy.
a. How efficient is each transfer?
b. What is the overall energy efficiency of the iPod?
[2]
[3]
8. Rachel uses 24 kJ of energy drying her hair with a hairdryer. The hairdryer is 45% efficient.
How much energy is wasted transferred as sound?
Energy efficiency questions
L
1. A roller coaster at the top of the ride is a gravitational potential energy store. As it goes
down the track its kinetic energy store increases (a useful energy transfer), and the
gravitational potential store empties.
Which stores of energy are increased due to wasted energy transfers? [2 marks] [grade 2]
2. A ball storing 10 J of gravitational potential energy is dropped to the floor. After bouncing
back up, the ball’s store of gravitational potential energy at its highest point has reduced
to 7 J.
a. How much energy has been wastefully transferred as the ball bounced? [1]
b. What is the efficiency of the ball as it bounces?
[2]
3. A kettle transfers 1,500 J of energy, 1,200 J to a thermal energy store in the water and
300 J to the air as sound. How efficient is the kettle?
4. Playing on an Xbox 360 transfers 102 J of energy each second. 9 J of this energy is
transferred to a thermal energy store. How efficient is the Xbox?
[2]
5. A pendulum with a store of 100 J of gravitational potential energy transfers 99.5J to a
kinetic energy store on its first swing.
a. How much energy is being wasted due to friction by transfer to a thermal energy
store?
[1]
b. How efficient is the pendulum?
[2]
6. What is the energy efficiency of a car that transfers 15 kJ of the chemical energy stored in
its petrol into 3,000 J of kinetic energy stored in its movement?