# Shm help

1. Dec 6, 2006

### bobbarkernar

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

Astronauts in space cannot weigh themselves by standing on a bathroom scale. Instead, they determine their mass by oscillating on a large spring. Suppose an astronaut attaches one end of a large spring to her belt and the other end to a hook on the wall of the space capsule. A fellow astronaut then pulls her away from the wall and releases her. The spring's length as a function of time is shown in the figure.
http://session.masteringphysics.com/problemAsset/1001073/9/knight_Figure_14_36.jpg

What is her speed when the spring's length is 1.2 ?

2. Relevant equations

3. The attempt at a solution

i tried to write the position as x(t)= .6+1.4sin((2pi/T)t)

2. Dec 6, 2006

### Staff: Mentor

The center of the sine wave is at 1.0m, not at 0.6m

Re-write the position equation with a number for T, then differentiate and figure out what phase to plug into the velocity equation. You're good to go!

3. Dec 6, 2006

### nrqed

Yes...Keep going. To find the speed you have to differentiate your equation, find the time corresponding to a position of 1.2 , plug that time in your equation for the velocity and get your answer. (you may read the period T from your figure)

Patrick

EDIT: I just noticed on the figure that the oscillation is from 0.6 to 1.4, so the equation should be $1+ 0.4 sin ({2 \pi \over T} t )$

Last edited: Dec 6, 2006
4. Dec 6, 2006

### bobbarkernar

so i should differentiate $1+ 0.4 sin ({2 \pi \over T} t )$
for t and Tshould be 3??

5. Dec 7, 2006

### Staff: Mentor

Yep, that's the next step.