1 \begin{problem*}{20.21}
2 The potential in a region between $x=0$ and $x=6.00\U{m}$ is $V =
3 a+bx$, where $a = 10.0\U{V}$ and $b = -7.00\U{V/m}$. Determine
4 \Part{a} the potential at $x = 0$, $3.00\U{m}$, and $6.00\U{m}$; and
6 \Part{b} the magnitude and direction of the electric field at $x =
7 0$, $3.00\U{m}$, and $6.00\U{m}$.
8 \end{problem5} % problem 20.21
12 Simply plugging into their $V(x)$ formula
14 V(0\U{m}) &= \ans{10.0\U{V}} \\
15 V(3.00\U{m}) &= 10.0\U{V} - 21.0\U{V} = \ans{-11\U{V}} \\
16 V(6.00\U{m}) &= 10.0\U{V} - 42.0\U{V} = \ans{-32\U{V}}
20 Using $E_x = -dV/dx$ we have
22 E = - \frac{d}{dx}(a+bx) = -b = \ans{7.00\U{V/m}}
24 At any point for $0 \le x \le 6.00\U{m}$.