Suppose a person tosses 17.2 kg of hay up 1.6 m to a hayloft once every 2.9 s. H
ID: 1335180 • Letter: S
Question
Suppose a person tosses 17.2 kg of hay up 1.6 m to a hayloft once every 2.9 s. How much work is the person doing with each toss? In J and in Watts? The maximum sustainable mechanical power a human can generate is roughly 1/3 horsepower. How much power is this person expending measured in horsepower? Look up horsepower in your textbook or the National Institute of Technology website How much mechanical energy does the person expend in one hour? How much energy is that in "food calories" (kilocalories in physics)?
Explanation / Answer
work = (17.2) (9.81) (1.6)
= 269.97 J
power = work / time
= 269.97 / 2.9
= 93.093 Watt
The maximum sustainable mechanical power a human can generate is roughly (1/3) horsepower
1 horse power = 746 Watt
(1 / 3) horse power = (1 / 3) 746 Watt
= 248.66 Watt
person power expending measured in horsepower is = (93.093 / 746)
= 0.124 horse power
energy expend in 2.9 s is 269.97 J
in hour energy expend wili be (1241.37 x 269.97) = 335135 J = 335.135 kJ
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