# Find the displacement.

1. Apr 15, 2012

### ScienceGeek24

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

What is the displacement at position x=0 and t=0?

2. Relevant equations

y(x,t)=Asin(kx-wt+phi)

3. The attempt at a solution

y=0.2m[0.18-90]=-0.199m

the answer is -.141 m help?

2. Apr 15, 2012

### Staff: Mentor

Where did the 0.18 come from? x = 0.

And don't mix radians and degrees. And don't forget the sine.

Last edited: Apr 15, 2012
3. Apr 15, 2012

### hypnosam

As the above post said, the displacement is 0. This is because at x=0, t= 0, so everything in the sin function becomes 0. Sin of 0 is 0. Hence the displacement =0

4. Apr 15, 2012

### ScienceGeek24

the displacement can't be 0 because the answer sheet says is -.141m and when i put x=0 i still get the same asnwer -0.199m don't get it.

5. Apr 15, 2012

### Staff: Mentor

The value of x is 0, not the displacement (which is the y value).
Show exactly what you did.

6. Apr 15, 2012

### hypnosam

Silly me, forgot the phase of the thing. Since everything else in the sin =0, then sin(-pi/4) =-1/(sqrt(2) multiply this by 0.2 and you get your answer of -0.141m.

7. Apr 15, 2012

### ScienceGeek24

Never mind what i was doing was wrong i was subtracting .18-90 and the sine of that time 0.2m is .199m

but what hypnosam is doing seems right

I did y= 0.2sin[0.18(0)+90(0)-pi/4] but i just don't know how he got 0.707 when inmy calculator i get 0.013 for sin(-pi/4) wth.

8. Apr 15, 2012

### Staff: Mentor

Make sure you're using radian mode.

9. Apr 15, 2012

### ScienceGeek24

got it thanks!