# Homework Help: SHM and Circular Motion Problem

1. Jun 2, 2014

### acomet

Q: During an earthquake, a skyscraper is designed to sway back and forth with simple harmonic motion with a period of 8 secs. The amplitude at the top floor of a particular earthquake is 70 cm. With respect to the simple harmonic motion of the top floor, calculate the following quantities:

a) The radius of the circle used to represent the SHM
b) The speed of the object moving round the circle
c) The angular velocity
d) The maximum speed at the top floor

I am in particular confused about part a). Would the solving of this question require the use of circular motion equations as well, or would SHM-related equations be enough to answer this?

2. Jun 2, 2014

### Simon Bridge

Neither - it does not require any equations at all - only geometry.

You should not be doing these problems by trying to remember which equation goes where.
How does a circle represent SHM?

3. Jun 2, 2014

### BiGyElLoWhAt

Can you express the motion of the top floor as a function of time? I think if you wrote it out, It might be more obvious what you're looking for...

*HINT* Think unit circle...

4. Jun 2, 2014

### acomet

So would the radius of the circle be equal to the amplitude?