# Stuck on Wave Motion Problem

1. Dec 30, 2004

### Klinger

I've looked at the following problem several times and have gotten stuck.

The Problem
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An earthquake-produced suface wave can be approximated by a sinusoidal transverse wave. Assuming a frequency of 0.50 Hz (typical of of earthquakes, which actually include a mixture of frequencies), what amplitude is needed so that objects begin to leave contact with the ground?

My Thoughts So Far
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To leave the ground acceleration must be 9.8 m/s^2. The equation of motion is x = A cos 2 Pi f t, where A is amplitude, f is frequency and t is time. I'm not sure how go from this point to get the equation for acceleration.

What's the next step?

2. Dec 30, 2004

### Gokul43201

Staff Emeritus
Find the second derivative of x with respect to t, and that's your acceleration.

Then, you want to find the maximum value that this can take, which is easy, since trigonometric functions are bounded.