A 715N person walks up three flights of stairs, covering a total vertical distance of 10.5(a)If as typical, only 20% of the caloric (food) energy is converted to work by the muscles, how many joules and food calories of energy did the person use

The answer is Five times the potential energy increase.

I assume the 10.5 is in meters. You need to include the units.

The number you end up with will be in Joules. That will need to be converted to (food) Calories.

1 food Calorie = 1000 calories = 4184 Joules.

To calculate the energy used by the person while walking up the stairs, you'll need to multiply the work done by the person by the conversion factor. Work is calculated by multiplying the force applied by the person by the vertical distance traveled.

First, let's calculate the work done by the person:
Work (W) = Force (F) × Distance (d)

Given:
Force (F) = 715N
Distance (d) = 10.5 meters

W = 715N × 10.5m = 7507.5 Joules

Now, since only 20% of the caloric energy is converted to work by the muscles, we can calculate the total energy used in calories by dividing the calculated work (in Joules) by the conversion factor.

Conversion Factor: 1 calorie = 4.184 Joules

Energy Used in Calories = (Work in Joules) / (Conversion Factor)
Energy Used in Calories = 7507.5 Joules / 4.184 cal/Joule

Energy Used in Calories = 1794.09 calories

Therefore, the person used approximately 7507.5 Joules or 1794.09 calories of energy while walking up the stairs.