Imagine a road on which the speed limit is specified at every single point. In
other words, there is a certain function \(L\) such that the speed limit \(x\)
miles from the beginning of the road is \(L(x) .\) Two cars, \(A\) and \(B\), are
driving along this road; car \(A\) 's position at time \(t\) is \(a(t),\) and
\(\operatorname{car} B^{\prime}\) s is \(b(t).\)
(a) What equation expresses the fact that car \(A\) always travels at the speed
limit? (The answer is not a' \((t)=L(t)\).)
(b) Suppose that \(A\) always goes at the speed limit and that \(B\) 's position
at time \(t\) is \(A\) 's position at time \(t-1 .\) Show that \(B\) is also going at
the speed limit at all times.
(c) Suppose, instead, that \(B\) always stays a constant distance behind A.
Under what conditions will \(B\) still always travel at the speed limit?