Question

A car is moving on a plane inclined at ${30}^{\circ }$ to the horizontal with an acceleration of $9.8m/s^2$ parallel to the plane upward. A bob is suspended by a string from the roof. The angle in degrees which the string makes with the vertical is: (Assume that the bob does not move relative to car and $g=9.8m/s^2$)

• A. ${20}^{\circ }$
• B. ${30}^{\circ }$
• C. ${45}^{\circ }$
• D. ${60}^{\circ }$

Answer 1

The correct option is B ${30}^{\circ }$

From frame of car, the effective acceleration $\left(g_{eff}\right)$ due to gravity shall be measured as shown in figure. Hence $g_{eff}$ makes an angle ${30}^{\circ }$ with vertical direction (down wards). Since the string aligns with direction of $g_{eff}$ in equilibrium, the required angle is $\theta ={30}^{\circ }$