Suppose you wanted to break a meter stick over your knee. The cross section of a meter stick is rectangular. Will it be easier to break with a.) the long side against your knee b.) the short side against your knee?

A.) The long side against your knee. The reason for this is explained by force, distance and work. Newton's equation W = fd (cos*) states that work is only done if the force and the distance are travelling parallel to each other. If the force and distance traveled is perpendicular, no work is done, in other words no energy is expended in Joules. So, if the meter stick is brought done perpendicular to the knee, no energy will be expended and it will be broken easily.