Question

A car is moving on a plane inclined at 30º to the horizontal with an acceleration of 9.8 m/s² 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) [g = 9.8 m/s² ]

(A) 20º 

(B) 30º 

(C) 45º 

(D) 60º

Answer 1

Correct option (B) 30º

Explanation: 

From frame of car, the effective acceleration (ge_ff) due to gravity shall be measured as shown in figure. Hence g_eff makes an angle 30° with vertical direction (down wards). Since the string aligns with direction of g_eff in equilibrium, the required angle is = 30°