- #1

Terp

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Hi everybody, this problem is giving me trouble and I was wondering if you could give me any advice.

The velocity of an object in simple harmonic motion is given by vx(t)= - (0.35 m/s)sin(20t + pi), where t is in s.

What is the first time after t=0s at which the velocity is - 0.25 m/s?

See the equation above.

I simply plugged -.25 m/s in for vx(t) above and solved for t, so I got:

-0.25 = -0.35sin(20t + pi)

.714 = sin(20t + pi)

When I solve for t I get t = -.397e-1 = -.0397s, but mastering physics (the program I use to do homework online) say it's wrong. I entered the answer as positive. Anybody have any idea? Thanks a lot!

edit: I just went to see my professor and he helped me set it up, when finished we had sin(20t) = -5/7, but master physics says it's wrong.

## Homework Statement

The velocity of an object in simple harmonic motion is given by vx(t)= - (0.35 m/s)sin(20t + pi), where t is in s.

What is the first time after t=0s at which the velocity is - 0.25 m/s?

## Homework Equations

See the equation above.

## The Attempt at a Solution

I simply plugged -.25 m/s in for vx(t) above and solved for t, so I got:

-0.25 = -0.35sin(20t + pi)

.714 = sin(20t + pi)

When I solve for t I get t = -.397e-1 = -.0397s, but mastering physics (the program I use to do homework online) say it's wrong. I entered the answer as positive. Anybody have any idea? Thanks a lot!

edit: I just went to see my professor and he helped me set it up, when finished we had sin(20t) = -5/7, but master physics says it's wrong.

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