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Chapter 14.1 Review: Work and Power
Transcript of Chapter 14.1 Review: Work and Power
doing work. REVIEW Energy, Work and Power Example Questions Example Answers James Watt and Horsepower Calculating Power SI Units What is power? What is work? SI Units Calculating Work Work: The product of
force and distance. Work Requires Motion
For a force to do work on an object, some of the force must act in the same direction as the object moves. If there is no movement, no work is done.
Work Depends On Direction
Any part of a force that does not act in the direction of motion does no work on an object. Written Formula:
Work = Force x Distance
W = F x D Doing work at a faster rate requires more power.
To increase power, you can increase the amount of work done in a given time, or you can do a given amount of work in less time. Written Formula:
Power = Work / Time
P = W / T Power: Watt (W)
Work: Joule (J)
Time: Second (s) One horsepower is equal to about 746 watts.
The horsepower was first defined by Scottish scientists James Watt (1736-1819).
-Watt was looking for a way to compare the power inputs of steam engines he had designed.... Horse were a logical choice for comparison as they were the most commonly used source of power in the 1700s.
-Watt defined the horsepower based on a very strong horse. 1. A desk exerts an upward force to support a computer resting on it. Does this force do work? Explain.
2. Two cars have the same weight, but one of the cars has an engine that provides twice the power of the other. Which car can make it to the top of the mountain pass first? Which car does more work to reach the pass?
3. You can carry two heavy bags of groceries up to your kitchen. Will you do more work on the bags if you carry them one at a time? Explain. 1. The supporting force does no work, because the object it acts on (the computer) does not move.
2. The car with the more powerful engine will reach the top first. Both cars do the same amount of work to reach the top.
3. Carrying one bag at a time uses only half the force, but requires that the force be applied through twice the distance. The work done is the same in both cases. Work: Joules (J)
Force: Newtons (N)
Distance: Meters (m)