Answer
The minimum radius is 21 cm
Work Step by Step
$F = \frac{mv^2}{r}$
$F = qvB$
We can equate the two expressions for $F$ to find the minimum required value for $r$:
$\frac{mv^2}{r} = qvB$
$r = \frac{mv}{qB}$
$r = \frac{(1.67\times 10^{-27}~kg)(1.0\times 10^7~m/s)}{(1.6\times 10^{-19}~C)(0.50~T)}$
$r = 0.21~m$
The minimum radius is 21 cm
