# Homework Help: Simple harmonic motion

1. Apr 20, 2012

### Mdhiggenz

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

An object is undergoing simple harmonic motion with frequency = 3.2 Hz and amplitude = 0.12 m. At = 0 the object is at = 0. How long does it take the object to go from = 0 to = 7.2×10−2 m?

2. Relevant equations

3. The attempt at a solution

s(t)=Asin(ωt)

A=amplitude=.12 m
ω=2πf=2π*3.2=20.1
t=undefined
s(t)=.12sin(20.1)
7.2*10^-2=.12sin(20.1t) divide out the .12
.6=sin(20.1t) Take the inverse sin of both sides
arcsin.6=20.1t The inverse of sin cancels out sin on the right so 20.1t is left.
36.87=20.1t Divide out 47.75 to get t.
t=1.8338 seconds

They want the answer in two figs, I put 1.8, and they marked it wrong are my steps wrong?

2. Apr 20, 2012

### Andrew Mason

Your method is correct. But watch your units. The arcsin of .6 must be expressed in radians. You are using degrees.

A good way to approach this kind of problem is to estimate it first. You can tell that it will be less than 1/4 of a cycle, and there are 3.2 cycles in one second, so it is a lot less than a second.

AM