Q.
The period of oscillation of simple pendulum of length l
suspended from the roof of the vehicle which moves without
friction, down an inclined plane of inclination α, is given by
We are given that the simple pendulum of length l is hanging from the roof of a vehicle which is moving down the frictionless inclined plane.
So, it's acceleration is gsinθ. since vehicle is accelerating a pseudo force m(g sin θ) will act on bob of pendulum which cancel the sinθ component of weight of the bob.
Hence we can say that the effective acceleration would be
equal to geff=gcosα
Now the time period of oscillation is given by T=2πgeffl=2πgcosal