A van accelerates uniformly down an inclined hill going from reast to `30m//s` in `6s`. During the acceleration , a toy of mass `m=0.1kg` hangs by a light string from the van's ceiling . The acceleration is such that string remains perpendicular to the ceiling. `(` Take `g=10m//s^(2))`

The angle `theta ` of the incline is `:`