Example 5: Pushing a Lawnmower

A lawnmower is moved horizontally (in the x direction) a distance of 10 feet. Find the work done if the lawnmower is pushed by a force F where

(a)    |F| = 15 pounds, θ = 30°. (See Figure 10.4.2a.)

Figure 10.4.2 (a)

(b)     F = 8i - 5j, in pounds. (See Figure 10.4.2b.)

Figure 10.4.2 (b)

(a)    cos θ = ½√3. |S| = 10.

W = |F| |S| cos θ = 15 · 10 · ½√3 = 75√3 ft lbs.

(b)     W = F · S = 8 · 10 + (-5) · 0 = 80 ft lbs.