Work
Work
Example: For me to jump 2 feet in the air, if I weigh 165 pounds, takes
W = Fs = 165(2) = 330 foot pounds.
Hook's Law For a spring
where d is the distance the spring is from its equilibrium point,
F is the
force exerted to compress to that distance, and k is a proportionality
constant. Example To compress a spring 2 inches from its equilibrium
point requires 50 pounds of force. How much work is it to compress
the spring an additional 2 inches? Solution We first find k:
50 = k(2)
We have
Example:
Sending a Rocket to Mars
Solution
We have that
Emptying a Tank
We use the
formula The distance that water y feet above the ground must be
pumped is We have
Lifting a Chain
Example A 2,000 lb car has gone over a 100 foot cliff at the pass. A crane lifts up to car with a chain that is 10 lbs per foot. How much work is done? Solution:
Work for the car = 2,000(100)
. Hence the total work is
200,000 + 50,000 = 250,000 ft lbs.
Running an Automobile
An automobile is run by a piston which turns the wheel. We have the equation Force = pressure (lbs/sq inch) times Volume ( cu inches) = (pressure)(p r^{2}) Boyle's Law states that the pressure is inversely proportional to the volume: P = k/V Hence
k But Hence the total work is
Example Solution
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