### Energy - Holy Cross High School

```National Physics
Electricity and Energy Homework
Section 4 – Energy
1
10 marks
Homework 1: Power stations
1. The sketch shows a block diagram of a coal-fired (thermal) power station.
BOILER
TURBINE
GENERATOR
NATIONAL
GRID
State the main energy change that occurs at each of the 3 parts. (3)
2.The transformer shown below allows a computer to operate properly from the
230 V mains.
4600
100
turns
turns
230 V ac
Computer
(a) State a transformer's function. (1)
(b) Copy the above diagram and label the core, primary coil & secondary
coil. (2)
3. A power station generates electricity at 25 kV. This voltage is stepped up to
275 000 V for the National Grid by a transformer as shown below. A few
hundred miles away, another transformer in a substation steps the voltage
back down for the local grid.
25 kV
12 000
turns
Power station
132000
275 000 V
turns
National Grid
55 000
2200
turns
turns
Local grid
(a) Why are such large voltages used for the National Grid? (1)
(b) If the lines have a resistance of 0.03Ω per metre what is the power loss
over a line 4km long? (3)
2
10 marks
Homework 2:
1. What is work done? Your answer should not be an equation! (1)
2. Calculate the work done by a horse when it uses a force of 800 N to pull a
sled a distance of 150 m.( 3)
3. Sean pushes Anthony in his go cart with a constant force of 700N doing 5.6kJ
of work. Calculate the distance travelled. (3)
4. When Jade pushes a wheel barrow she does 0.8kJ of work. If she pushes the
barrow 120cm. Calculate the force applied. (3)
3
10 marks
Homework 3
1. Name one quantity the potential energy of an object depends on? (1)
2. Calculate the potential energy of a 45g ball stuck up a 1.8m tree. (3)
3. If the work done of a diver of mass 65kg is 16kJas he dives from the high board
calculate the height of the board. (3)
4. A strong man lifts a set of weights 2m. If the energy transferred is 1.65kJ calculate
the mass of the weights. (3)
4
10 marks
Homework 4
1. Name one quantity the kinetic energy of an object depends on. (1)
2. A jogger of mass 60kg runs at 5ms-1. Calculate his kinetic energy.(3)
3. A paper aeroplane of mass 1g has a kinetic energy of 25mJ. Calculate its
speed.(3)
4. A bullet has a speed of 1200ms-1 and a kinetic energy of 11.5kJ. Find its mass.
(3)
5
10 marks
Homework 5
1. A roller coaster carriage has a mass of 300 kg when it is carrying a full load.
(a) Calculate the potential energy of the carriage when it is at the top of a drop
of 30m above the ground.(3)
(b) At the bottom of the drop it is at a height of 2 m above the ground.
Calculate its potential energy now.(3)
(c)Calculate how much kinetic energy the carriage will have at this point. (1).
2. A 30g ball is dropped through a height of 2m. Calculate its speed just as it hits
the ground. (3)
6
10 marks
7
10 marks
```