In the past, salmon would swim more than 1130 km (700 mi) to spawn at the headwa

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.

A) What is the total energy used by a 2.5-kg salmon while making this 22-day trip?

Express your answer to two significant figures and include the appropriate units.

B) 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 Jof energy.

Express your answer to two significant figures and include the appropriate units.

C) 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?

Express your answer to two significant figures and include the appropriate units.

Explanation / Answer

energy consumed rate is P/m= 2w/kg

a)

power for 2.5 kg is,P=(2*2.5)=5 W

time t=22day=(22*24*60*60) sec

total energy E=P*t

E=5*(22*24*60*60)=9.5*10^6 J

b)

here,

80% above energy is due to burning of fat,

and

1g of fat releases 3.8*10^4 J of energy

now,

mass of the fat burned is,

m=(0.8*9.5*10^6)/(3.8*10^4)

m=200 g

c)

mass of the remaining fat is ,

m=(15% of 2.5 kg)- (mass of burned fat)

m=(0.15*2.5*10^3-200)

m=175 g

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