# Work done and power

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When a force moves an object through a distance, work is said to be done. Work done is the energy transferred and it can be calculated using the formula: Work Done = Force Ă Distance moved in the direction of the force. It is measured in Joules, J.

Power is defined as the rate of energy transfer and is measured in Watts, W. It can be calculated using: Power = energy transferred/time.

A force-displacement graph is drawn by plotting the force acting on an object on the y-axis and the distance travelled on the x-axis. The area under the plotted graph is equal to the work done on or by the object.

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A drop tower at an amusement park has a power of 253000 W. Given that the total mass of the ride and passengers is 9500 kg, calculate the time taken by the drop tower to raise the passengers to a vertical height of 15 m. Use g = 9.8 m/sÂ˛.

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A pump delivers 85 kg of water and pumps it upwards to a vertical height of 43 m in 6 minutes. Calculate the power of the pump. Use g = 9.8 m/sÂ˛.

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A light bulb of power 100 W is left on for an hour. Calculate the energy used by the light bulb in the one hour.

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A car of mass 1000 kg and power 74570 W is travelling at a constant speed of 12 m/s for 45 seconds. Calculate the driving force of the car.

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An electric motor of power 150 W raises an object for a vertical height of 1.5 m at a constant velocity of 3 m/s. Using g = 9.8 m/sÂ˛, find the mass of the object.

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Sketch a force-displacement graph for a car that exerts a constant driving force of 1500 N for 8 m in the forward direction.

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The force-displacement graph for an object is given. Calculate the work done by the object during its motion.

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An object is travels for 5 m by exerting a constant forward force of 23 N. It then decreases the force it is exerting to 0 at a constant rate. The object travels another 3 m while doing this. Plot a force-displacement graph for the object.

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A force-displacement graph is plotted for the motion of an object. Given that the area under the graph is 1500 NmÂ˛ and that the object is exerting a constant force of 35 N, calculate the distance the object travels.

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A force-displacement graph is plotted for the motion of an object of a distance 7 m. Given that the area under the graph is 870 NmÂ˛ and that the force exerted by the object is constant, calculate the force exerted by the object.

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An object travels as shown by the force-displacement graph given. Calculate the work done by the object.

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An object travels as shown by the force-displacement graph given. Given that the area under the first section of the graph is 75 J, the area under the second section of the graph is 300 J and that the total work done by the object is 425 J, find the total distance travelled in the third section of the graph.

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An object travels as shown by the force-displacement graph given. Given that the area under the second section of the graph is 720 unitsÂ˛, the area under the third section of the graph is 120 unitsÂ˛ and that the total work done by the object is 1340.5 J, find the inital force exerted by the object.

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A car produces a driving force of 1800 N and travels 12 m in the direction of the force. Calculate the work done by the car.

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A runner produces a force of 47 N in the forward direction and runs at a constant speed for 5 m. Calculate the work done by the runner.

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A man is pushing a shopping trolley of weight 330 N with a horizontal force of 50 N. He pushes the trolley 3.2 m forward at a constant velocity. Calculate the work done by the man.

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A cat climbs up a 7 m wall at a constant velocity. Given that the work done by the cat is 860 J, calculate the force on the cat.

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A boy pushes a box of mass 7 kg with a constant horizontal force of 30 N for 2.5 m. He then pushes a box of 10 kg with the same constant horizontal force for the same distance of 2.5 m. Which box does the boy do more work on?

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A bodybuilder lifts a bar of 100 kg from the floor for a distance of 2.35 m. Calculate the work done by the bodybuilder. Use g = 9.8 m/sÂ˛.

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A man tries to push on a leg press machine set at 80 kg with a force of 40 N, but fails and the machine does not move. What is the work done by the man?

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Explain why more work will need to be done to push a box forward for the same distance with the same force, when the force is at an angle to the horizontal.

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The work done by a car moving forward for 2 minutes is 1560000 J. Calculate the power of the car.

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A car has a power of 14500 W. It travels a distance of 5 m in 1.5 minutes. Calculate the driving force acting on the car.

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A ski lift lifts its passengers through a vertical height of 600 m in 7 minutes. Given that the total mass of the ski lift and the passengers is 8000 kg, calculate the power of the ski lift. Use g = 9.8 m/sÂ˛.

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