You curl a 5.5-kg (12 lb) barbell that is hanging straight down in your hand up

Question

You curl a 5.5-kg (12 lb) barbell that is hanging straight down in your hand up to your shoulder.

A) If the body is 20% efficient at converting chemical energy into mechanical energy, how many times would you have to lift the barbell in order to burn enough calories to use up the energy absorbed by eating a 300-food-calorie dish of ice cream? Note: 1 food calorie = 1 kilocalorie = 4186 J.

B) If the body is 20% efficient at converting chemical energy into mechanical energy, how many times would you have to lift the barbell in order to burn enough calories to use up the energy absorbed by eating a 300-food-calorie dish of ice cream? Note: 1 food calorie = 1 kilocalorie = 4186 J.

Explanation / Answer

work = force * distance = (mass * g) * distance = (5.5 Kg * 9.8 m/s^2) * (1 m) = 53.9 Nm = 53.9J

Power = work / time = 53.9 J/ 0.3s = 179.67 W

energy to be burned by eating ice cream = 300 food calories * 4186 J/foodcalorie = 1.2558MJ
Each time you lift barbell, you burn 53.9J.
If efficiency was 100%, then have to lift barbell 1.2558MJ/53.9J times = 23298.7 times. Since the efficiency of chemical to mechanical conversion is only 20%, have to work a lot harder to burn off the icecream. Have to lift barbell:
1.2558MJ/53.9J/0.2 = 116493.5 times. So round up to 116494 times.

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