Question

Rowan's and Jean's rates of energy consumption (which equals the power expended) doing various activities are given below. (Values from Table 7.5 in Urone and J. Appl. Physiol., 75, p2514-2520, 1993).

ROWAN
Activity Rate of energy consumption
Sleeping 75 w
Sitting 110 w
Studying 120 w
Walking 280 w
Cycling 400 w

Jean
Activity Rate of energy consumption
Sleeping 55 w
Sitting 95 w
Studying 105 w
Walking 280 w
Cycling 400 w

(a) What are Rowan's daily energy needs in both kJ and kcal if his day consists of sleeping for 8hrs, walking for 2hrs, studying for 10 hrs, cycling for 0.5hrs and sitting for 3.5hrs ?

Answer 1

Rowan's daily energy needs are calculated by multiplying each activity's power expenditure by the time spent on the activity and summing them up to get a total in watt-hours, which is then converted to kilojoules and kilocalories to provide both energy measurements.

Step-by-step explanation:

To calculate Rowan's daily energy needs, we need to multiply the rate of energy consumption for each activity by the time spent on that activity, and then sum the results:

• Sleep: 75 W × 8 hrs = 600 Wh
• Walking: 280 W × 2 hrs = 560 Wh
• Studying: 120 W × 10 hrs = 1200 Wh
• Cycling: 400 W × 0.5 hrs = 200 Wh
• Sitting: 110 W × 3.5 hrs = 385 Wh

Now we add the energy consumption for all activities together: 600 Wh + 560 Wh + 1200 Wh + 200 Wh + 385 Wh = 2945 Wh. To convert Wh to kJ, we use the conversion factor 1 Wh = 3.6 kJ. Therefore:

Rowan's daily energy needs = 2945 Wh × 3.6 kJ/Wh = 10602 kJ.

To convert kJ to kcal, we use the conversion factor 1 kJ = 0.239006 kcal. Hence:

Rowan's daily energy needs = 10602 kJ × 0.239006 kcal/kJ = 2533.78 kcal (rounded to two decimal places).