What Frequency Causes a Rock to Lift Off a Vibrating Platform?

[aubailey]

Homework Statement

A vibration platform oscillates up and down with an amplitude of 10.4 cm at a controlled variable frequency. Suppose a small rock of unknown mass is placed on the platform. At what frequency will the rock just begin to leave the surface so that it starts to clatter?

Homework Equations

ax(t) = -w^2 * Asin(wt)

The Attempt at a Solution

I know I need to find the acceleration with the given amplitude but i still have two variables, omega and time in order to find that. Can anyone point me in the right direction?

 

[tiny-tim]

welcome to pf!

hi aubailey! welcome to pf!

what is your basic equation, the one that determines whether the rock loses contact (ie the reaction force is zero)?

 

[aubailey]

Yes, how do I find the frequency that will cause the rock to be lifted a little?

i suppose it is similar to a rollercoaster problem but I am kind of stuck because I am only given the amplitude.