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Published byJeffrey Payne Modified over 8 years ago
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TopicSlidesMinutes 1 Displacement 927 2 Vectors 1339 3 Kinematics 1339 4 Graphs 1030 5 Energy 1030 6 515 7 Springs 412 8 Shadows 39 9 Field of Vision 721 10 Colors 39 11 Concave mirrors 721 12 Convex mirrors 412 13 Refraction 515 14 Lenses 1030 15 Optical Power 618 Power
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Click Power is the rate of doing work. It tells us how fast work is being done. Power is important in order to establish the “speed” with which a given force acts. The formula for power is: Velocity Where: P = power in watts (W) F = force in newtons (N) t = time in seconds (s) v = velocity in m/s
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A 20 kg object is pushed 15 m along a horizontal frictionless surface by a horizontal force of 8 N. If the work was done in a time of 12 s, calculate: Click a) The work done. 120 J Click b) The power output. 10 W c) What becomes of the work done? It is lost to overcome friction (in the form of heat and sound) Click Power Slide: 6. 16. 1 Note that we assume the object is moved at constant velocity.
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What power is required to raise a mass of 40 kg a distance of 5 m in a time of 2 s? Click Power Slide: 6. 26. 2
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A 2 000 kg elevator is raised a distance of 18 m in a time of 40 s. Determine: Click a) The work done. 3.6 x 10 5 J Click b) The rate of doing work. 9 x 10 3 W c) What becomes of the work done? It is gained by the elevator in the form of potential energy. Click Power Slide: 6. 36. 3
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If 700 W of power is needed to keep a boat moving through water at a constant speed of 10 m/s, what is the magnitude of the force exerted by the motor of the boat? Click Power Slide: 6. 46. 4
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Betty uses the hoist illustrated on the right to raise a mass of 200 kg. If she can pull the rope 5.0 metres in a time of 10 seconds, what is Betty’s power output? Note: Disregard friction. Click A) 17.0 W B) 100 W C) 163 W D) 980 W I.M.A. = 6 (6 ropes) Power Slide: 6. 56. 5
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… and good luck!
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