An air car moves up with acceleration a along a cable inclined at angle a to the horizontal, as shown in the figure. 

A pendulum hanging in equilibrium inside the cable car makes angle $\theta$ with the vertical. The value of $\tan \theta$ is.

From the frame of reference in the air car

The figure shows the forces acting on the pendulum. Using dynamics along the horizontal and the vertical, we have 

$\begin{array}{r}T\sin \theta =m(a\cos \alpha )\\ T\cos \theta -mg=m(a\sin \alpha )\end{array}$

Eliminating T, we have 

$\tan \theta =\frac{a\cos \alpha }{g+a\sin \alpha }$