Question

Calculate the energy in kcal used by a 55 kg woman who does 55 deep knee bends in which her center of mass is lowered and raised 0.400 m. (She does work in both directions.) You may assume her efficiency is 20%.

Answer 1

Answer:

Energy = 1.132887kcal

Explanation:

Given

Mass = 55kg

Knee bend = 55

Efficiency = 20%

Displacement = 0.4m

First, we'll calculate the total Workdone

Work done = 2n(mgh)

Where n = 55, m = 55kg, g = 9.8m/s² and h = 0.4m

Work done = 2 * 55 * 55 * 9.8 * 0.4

Work done = 23,716J

Since the woman's efficiency is 20% of her total work done;

Then, .her energy = 20% of 23,716J

= 4,743.2

= 4.74KJ

Energy in kcal = 1.132887kcal

Answer 2

Answer: 0.57Kcal

Explanation:

Given m= 55kg, g = 9.8m/s²

The Workdone is given by:

W = mg∆h

Where ∆h is the total distance covered

∆h = 55 ×0.4m = 22m

W = 55 × 9.8 × 22

W = 11,858 J

Since 1Kilocalorie = 4,186.80Joules

W = (11,858/4186.80) Kcal

W = 2.8322Kcal

But since her efficiency is 20%, (this means the conversion ratio between her chemical energy to mechanical ; potential energy), the

The efficient Energy used for the exercise is

Ew = 0.20 × 2.8322

Ew = 0.566 ~= 0.57Kcal