A car is moving on a plane inclined at $30^{\circ}$ to the horizontal with an acceleration of $10 \mathrm{~ms}^{-2}$ parallel to the plane upward. A bob is suspended by a string from the roof of the car. The angle in degrees which the string makes with the vertical is $\_\_\_\_$ . (Take $\mathrm{g}=10 \mathrm{~ms}^{-2}$ )