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P3d(ii) Work and Power You will find out about Power How to calculate Power Fuel consumption data
Power We previously learned that W=Fd so recall that work is done when a force is applied to an object and it moves a distance. No force applied or the object does not move in the direction of that force then no work is being done. But how does time fit into this? The faster the work is done the greater the amount of Power. He is faster so he has a greater Power. REMEMBER: Work Done = Force x Distance
Difficult Power Calculation There are 14 steps separated by 0.2m. Therefore the TOTAL DISTANCE from first step to top step is: 14 x 0.2m = 2.8m.
Re-arranging Power equation REMEMBER: Use the Triangle Rule when re-arranging equations with THREE variables! w P x t We know that W = F x d EXAMPLE: A car runs for an hour with its engine producing 0.5MW (0.5 Million Watts). Calculate the amount of Work Done. W = P x t W = 0.5 M x (60x60) W = 1,800,000,000J W = 1,800 MW The car’s engine provides a forward pull force of 25,000N at 25m/s. Calculate its power at this velocity. P = F x v P = 25,000N x 25m/s P = 500,000W or 0.5MW M or Mega = 1,000,000 Number of seconds in one hour
Fuel Consumption CarEngine Capacity in litres Power in kW Top speed in km/h City fuel consumption in litres/100 km Bugatti Veyron Vitesse Fiat 500 TwinAir Greater Power output so has a higher top speed. SMALLER engine means a BETTER fuel consumption. NOTE: The smaller the number the BETTER the fuel consumption. 5.1 means it only uses 5.1 litres of petrol to travel 100 km. The Veyron uses 37.2 litres of petrol to go the same 100 km which is a lot more so NOT a good fuel consumption. Petrol is EXPENSIVE so the Veyron would cost a lot more to run. When petrol is burned in a car it releases harmful carbon dioxide gas which is a major contributor to the greenhouse gases in our atmosphere. Scientists think this is leading to dramatic climate change. Car manufacturers as well as consumers are aware of this and so are interested in making cars that are eco-friendly. Therefore engines that are fuel-efficient and emit LESS greenhouse gases are encouraged.
Questions 1.A huge electromagnet lifts a 1,500kg car 15m high in 20 seconds. A different electromagnet lifts the same car the same height but in 15 seconds. Which electromagnet does more work? Which is most powerful and why? 2.Aaron has a weight of 600N and runs up 3,500 steps. Each step is 0.15m high. He does this in 15 minutes. Calculate his work done and his power. 3.A 150kW motor raises a 25,000N load a height of 10m. How long does it take? 4.A bus provides a forward force of 15,000N. When it travels at 15m/s what is its Power? 5.A hovercraft travels at 40km/h for 0.5 hours to get from Portsmouth to Ryde. If it operates at a Power of 0.75MW what is its forward force when travelling? (assume speed is constant and at maximum)