Why Does the Particle Not Move in the +x Direction at t = 0.13351 Seconds?

[inversesine]

Homework Statement

The position of a particle is given in cm by x = 6*cos(3πt), where t is in seconds.

What is the first time that the particle is at x = 0 and moving in the +x direction?

Homework Equations

The Attempt at a Solution

I set x=0, and divided 0 by 6, resulting in 0. From there, I took the inverse cosine of each side, leaving me with the equation (π/2)=3πt. Then I divided (π/2) by 3π, and was left with a t value of .13351 seconds. The problem is that when I submit that answer, it is incorrect.

 

[ehild]

Homework Statement

The position of a particle is given in cm by x = 6*cos(3πt), where t is in seconds.

What is the first time that the particle is at x = 0 and moving in the +x direction?

Homework Equations

The Attempt at a Solution

I set x=0, and divided 0 by 6, resulting in 0. From there, I took the inverse cosine of each side, leaving me with the equation (π/2)=3πt. Then I divided (π/2) by 3π, and was left with a t value of .13351 seconds. The problem is that when I submit that answer, it is incorrect.

You ignored that the particle moves in the +x direction: the velocity is positive.

How do you get the velocity of the particle at time t?

ehild