In creating his definition of horsepower, James Watt, the inventor of the steam

Question

In creating his definition of horsepower, James Watt, the
inventor of the steam engine, calculated the power output of a
horse operating a mill to grind grain or cut wood. The horse
walked in a 24-ft diameter circle, making, according to Watt,
144 trips around the circle in an hour. (a) Using the currently
accepted value of 746 watts for 1 horsepower, calculate the
force (in pounds) with which Mr. Watt’s horse must have been
pulling. (See Appendix D for useful conversion factors.)
(b) Calculate the power output, in hp, of a 70-kg human being
who climbs a 3.0-m-high set of stairs in 5.0 seconds.
How Do i solve for force in lbs in part a?

Explanation / Answer

1 hp = 746 W = 746 J/s

work done by horse = F*d*144 d= diameter = 24*0.3048 m

746J = F*3309.318

F = 0.2254 N

since 1 N = 0.224808 pound

F = 0.050671 pound

b.) power = work/time

= 70*9.81*3/5

= 686.7 J

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