A trolley is sliding down a frictionless slope having inclination è. If a simple pendulum is suspended on top of this trolley, its periodic time is given by
$ g^2 _{off} = a_x^2 + (g -ay ) ^2 here a_x g sin \theta cos \theta , ay = g sin ^2 \theta $ $ = a_x^2 + g^2 + a_y^2 - 2 ga_y $ $ = a^2 sin ^ 2 \theta cos ^2 \theta + g^2 + g^2 sin^2 \theta - 2 g^2 sin ^2 \theta $ $ = g^2 ( 1 -sin^2 \theta ) $ $= g ^2 cos ^2 \theta $ $ \therefore g_{eff} = g cos \theta $