# Homework Help: Vibrating Platform and Rock

1. Feb 19, 2012

### aubailey

1. The problem statement, all variables and given/known data
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?

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

3. 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?

Last edited: Feb 19, 2012
2. Feb 19, 2012

### 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)?

3. Feb 19, 2012

### 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.