In many countries, oxen, guided by children, plow straight, level furrows through soil. The ox of the figure pulls its plow a length of 200 meters in five minutes.

**Calculate** the least average horsepower expended by the ox.

♦ We have no way of knowing what friction force occur. To ignore friction is a major assumption. We ignore friction; our answer will be a "least power required." As system,
we take the soil removed from the furrow once the ox completes a furrow. The mass of soil tilled equals:

Ignoring friction, the Extrinsic Energy Equation applies: