Final answer:
To calculate the kilocalories expended by a 70kg man running at 7.5 mi/hr for 30 min, you need to use the formula: Kilocalories = Power (W) x Time (hrs) x Efficiency. By converting the speed to m/s and calculating the power, the kilocalories expended can be calculated to be approximately 1.379 kcal.
Step-by-step explanation:
To calculate the kilocalories expended by a 70kg man running, we need to use the formula:
Kilocalories = Power (W) x Time (hrs) x Efficiency
First, convert the speed from mph to m/s:
7.5 mi/hr = 7.5 x 1609.34 m/3600 s = 3.35 m/s
Next, calculate the power using the given information:
Power (W) = Weight (N) x Speed (m/s) = 70kg x 9.8 m/s^2 x 3.35 m/s = 2302 W
Given that the efficiency is 25%, we can calculate kilocalories:
Kilocalories = 2302 W x 0.25 x 0.0002388 kcal/W = 1.379 kcal