Answer:
Explanation:
The rock will begin to leave the surface when reaction force becomes zero or when the acceleration of the plate-form downwards and gravitational acceleration acting on mass m becomes equal .
acceleration of plate- form ( maximum ) = ω²A , A is amplitude and ω is angular frequency .
ω²A = g
4π² n² = g
n² = g / 4π²
9.8 / 4 x 3.14²
= .2484
n = .5