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

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SUMMARY

The position of a particle is defined by the equation x = 6*cos(3πt), where t is in seconds. The first time the particle is at x = 0 and moving in the +x direction is not at t = 0.13351 seconds, as initially calculated. To determine the correct time, one must also consider the velocity of the particle, which is derived from the position function. The velocity function, v(t) = -18π*sin(3πt), must be positive at the time when x = 0 to confirm that the particle is moving in the +x direction.

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inversesine
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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.
 
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inversesine said:

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
 

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