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Power, force and velocity

Power, force and velocity. Power is the rate at which a force does work. If an engine drives an object at velocity v by means of a force F in the direction of motion, the power developed by the engine Fv. The SI unit of power is the watt (W) 1 W is the rate f working of 1 J s -1.

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Power, force and velocity

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  1. Power, force and velocity Power is the rate at which a force does work. If an engine drives an object at velocity v by means of a force F in the direction of motion, the power developed by the engine Fv. The SI unit of power is the watt (W) 1 W is the rate f working of 1 J s-1.

  2. Power, force and velocity Example 1 A crane lifts a load of 60 kg to a height of 15 m at a steady speed of 0.5 ms-1. Find the power required. Work done against gravity = 60g  15 = 8828 J Time taken to lift load = 15  0.5 = 30 s Power P = 8828  30 = 294 W. Or Power P = F  v = 60g  0.5 = 294 W

  3. Power, force and velocity Example 2 A car of mass 800 kg moves at a steady speed of 12 ms-1 up a slope inclined to the horizontal at an angle 10. resistance forces total 600 N. Find the power output of the engine. DF – 800gsin10 – 600 = 0 DF = 1961 Work done in one second = P = 1961  12 = 23.5 kW

  4. Power, force and velocity Example 3 A pump raises water from a tank through a height of 2 m and outputs through a circular nozzle of radius 2 cm at 5 ms-1. Find the rate at which the pump is working. Volume of water =   0.022  5 = 0.0062832 m3 Mass of water = 0.0062832  1000 = 6.283 kg KE = ½ mv2 = ½  6.283  52 = 78.5375 J PE = mgh = 6.283  9.8  2 = 123.1468 J Total work done in one second = 202 J Rate of working = P = 202 W.

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