The wheel of radius `R` rolls without slipping on horizontal rough surface, and its centre `O` has an horizontal acceleration `a_(0)` in forward direction. A point `P` on the wheel is a distance `r` from `O` and angular position `theta` from horizontal. For a given values of `a_(0)`, `R` and `r`, determine the angle `theta` for which point `P` has no acceleration in this position.