Question

Measurements in the 1800s showed that a draft horse could provide a maximum steady output power over the course of a working day; that's how the "horsepower," about 750 W, came to be defined. Another animal that's used for pulling loads for which there are good data is the sled dog. A 38 kg dog can provide power to pull a sled with a force of 60 N at a steady 2.2 m/s. Dogs and horses have approximately the same 25% metabolic efficiency as humans. A horse is working steadily, providing 750 W of output power. How much food energy does the horse need to work for 1 hour, to the nearest MJ?

Answer 1

Solution:

Answer: 11 MJ

Mass = 38 kg

Force = F = 60 N

Velocity = v = 2.2 m/s

Power = 750 W

Time = t = 1 hour = 3600 s

Efficiency = 25 % = 0.25

Energy = E = P t = ( 750 ) ( 3600)( / 0.25) = 29700 Joules , taking the 25% efficiency.

= 10.8 MJ = 11 MJ (2 sign . digits)