In the past, salmon would swim more than 1130 km (700 mi ) to spawn at the headw
ID: 1341164 • Letter: I
Question
In the past, salmon would swim more than 1130 km (700 mi ) to spawn at the headwaters of the Salmon River in central Idaho. The trip took about 22 days, and the fish consumed energy at a rate of 2.0 W for each kilogram of body mass.
What is the total energy used by a 2.0-kg salmon while making this 22-day trip?
About 80% of this energy is released by burning fat and the other 20% by burning protein. How many grams of fat are burned? One gram of fat releases 3.8×104 J of energy.
If the salmon is about 15% fat at the beginning of the trip, how many grams of fat does it have at the end of the trip?
Explanation / Answer
a)
work = power * time
work = 2W/kg * 2.0kg * 22d * 24h/d * 3600s/h = 7.6 *10^6 J
Total Energy used = 7.6 MJ
b)
Total Energy by fat burn = 0.8 * 7.6 * 10^6 J
Fat mass burn, M = 0.8 * 7.6 * 10^6 / 3.8 * 10^4 J
Fat mass burn, M = 160 g
c)
Initial fat = 0.15 * 2.0 kg = 0.30 kg
Initial fat = 300 g
Fat Burned = 160 g
So at the end of the trip it has 140 g of fat.
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