Question

1. A typical human’s power rating for an entire day is 100 watts. How did your power rating when climbing stairs compare to that value? (Power ratings we got in lab, 226.8 W, 456.4 W, 251.7 W, 405.8 W)

2. How much total energy, in Joules, does a typical human burn in a day?

3. Given that there are 4,186 J/kcal, how many kcal of food energy does a typical human need to consume in a day?

4. An elevator motor produces 2,000 W. How much energy does it produce every second?

Answer 1

(1.) power rating when climbing stairs can be calculated by using the formula-

Power = (work done in climbing stairs in joules) / (time required to climb stairs in seconds) .......1

where workdone can be found from the formula

workdone (joules) = height of staircase (m) * weight of stair climber (N) = mgh

substituting in 1. we get,

power = mgh / t

and then compare it with the power rating for an entire day.

(2) The basal metabolic rate of a human is about1,300 - 1,500 kcal/day for an adult female &

1,600 - 1,800 kcal/day for an adult male.

i.e. standard result is 5.44 - 6.28 MJ (female) &

6.69 - 7.53 MJ (male)

(3) accordin to question,  

4186 joule per kcal

i.e 4186 joule = 1 kcal

so approx 1500 - 2000 kcal/day is required.

(4) power produced = 2000 W

since power = workdone (energy) / time

so in 1 second,

energy = 1 * 2000 = 2000 J