A block on a slope at different angles

Tilt a rough board slowly. At first the block stays put; past a certain angle it slides, faster and faster. You will make the program find the acceleration at every angle, for three surfaces, and the angle where each block starts to slide.

The idea. A block at rest starts to slide when $\tan\theta > \mu$. After that (taking $\mu_s = \mu_k = \mu$ for simplicity),

and before that, $a = 0$.

Your tasks.

1. Make accel(mu) return the acceleration at every angle in angles, zero where the block stays put.
2. Work out the angle of repose for each surface.
3. Find, for $\mu = 0.35$, the first angle in the list where the acceleration reaches $3.0\ \text{m/s}^2$.