Answer
a. $F(10) = 200$ lb.
$\frac{dF}{d\theta} = 50$ lb./rad.
b. $\mu = 4$ rad$^{-1}$
Work Step by Step
a. From the graph, we find $F(10) = 200$ lb.
To find $\frac{dF}{d\theta}$, we find the slope of the tangent line to the curve at $\theta = 10$. The tangent line crosses the points (6,0) and (14,400). Thus, $\frac{dF}{d\theta} = \frac{\Delta y}{\Delta x} = \frac{400-0}{14-6} = \frac{400}{8}=50$ lb/rad.
b.
$\frac{dF}{d\theta} = \mu F$
$\mu = \frac{dF}{d\theta} * \frac{1}{F} = \frac{200}{50} = 4$ rad$^{-1}$
