Answer
Over the interval (0,3), the angle y is equal to 0 at times $t = \frac{5}{6}, \frac{11}{6}, \frac{17}{6}$
Work Step by Step
If $y=0$, then $cos[\pi~(t-\frac{1}{3})] = 0$
Then: $\pi~(t-\frac{1}{3}) = \frac{\pi}{2}, \frac{3\pi}{2}, \frac{5\pi}{2},...$
$t-\frac{1}{3} = \frac{1}{2}, \frac{3}{2}, \frac{5}{2},...$
$t = \frac{5}{6}, \frac{11}{6}, \frac{17}{6},...$
Over the interval (0,3), the angle y is equal to 0 at times $t = \frac{5}{6}, \frac{11}{6}, \frac{17}{6}$
