Answer
a. $l_o$ is the length of the rod at a speed of 0.
b. $\lim_{v \to c^-} l(v) = 0$. The physical significance is that as the rod approaches the speed of light, its length approaches 0.
Work Step by Step
a. The function $l(v)$ is the length of a narrow rod as a function of $v$. Therefore, $l_0$ is the length of a narrow rod with $v=0$, or at a speed of $0$.
b. From Fig. Ex-31 given in the problem, $l$ approaches 0 as $v$ approaches $c$ from the left. Thus, $\lim_{v \to c^-} l(v) = 0$. The physical significance is that as the rod approaches the speed of light, its length approaches 0.
