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

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