Brain Power The human brain consumes about 22 W of power under normal conditions

Question

Brain Power The human brain consumes about 22 W of power under normal conditions, though more power may be required during exams.

Part A How long can one Snickers bar (280 Cal per bar) power the normally functioning brain? [Note: The nutritional calorie, 1 Cal, is equivalent to 1000 calories (1000 cal) as defined in physics. In addition, the conversion factor between calories and joules is as follows: 1 Cal = 1000 calories = 1 kcal = 4186 J]

Part B

At what rate must you lift a 3.6-kg container of milk (one gallon) if the power output of your arm is to be 22 W?

Part C

How long does it take to lift the milk container through a distance of 1.0 m at this rate?

Explanation / Answer

given power = P= 22W

energy E = 280 Cal = 280*1000 = 280000 calories

E = 280*4186 = 1172080 J

time for which snickers can power the brain = E/P

t = 1172080/22 = 53276.4 s

t = 14.8 hours

++++++++

part(B)

work done W = m*g*h

power P = W/t

P = m*g*h/t

h/t = P/mg

h/t = 22/(3.6*9.8)

rate at which the container is lifted = 0.623 m/s

part(C)

time = d/v = 1/0.623 = 1.61 s <<---------answer

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