An ice cream has a marked value of 700 kcal. How many kilowatt hour of energy will it deliver to the body as it is digested

To find the energy delivered to the body in kilowatt-hours (kWh) from the marked value in kilocalories (kcal), we can perform the conversion in two steps: first, convert kilocalories to Joules, and then convert Joules to kilowatt-hours.

Step 1: Convert kilocalories (kcal) to Joules (J)
Recall the relationship between calories and Joules:
1 calorie (cal) ≈ 4.184 Joules (J)
Therefore, 1 kilocalorie (kcal) is:
1 kcal = 1000 cal = 4.184 × 10³ J = 4184 J

Now, calculate the total energy in Joules for 700 kcal:
$E=700\times 4184\text{J}$
$E=2,928,800\text{J}$

Step 2: Convert Joules (J) to kilowatt-hours (kWh)
A kilowatt-hour is a unit of energy representing one kilowatt (1000 Watts) of power sustained for one hour (3600 seconds):
1 kWh = 1000 W × 3600 s = 3,600,000 J = 3.6 × 10⁶ J

To convert the energy from Joules to kilowatt-hours, divide the energy in Joules by 3,600,000 J/kWh:
$E=\frac{2,928,800}{3,600,000}\text{kWh}$
$E\approx 0.8136\text{kWh}$

Rounding to two decimal places, we get:
$E\approx 0.81\text{kWh}$

Thus, the ice cream will deliver approximately 0.81 kWh of energy to the body.