Particle Rotation: Solving for X Coordinate at a Given Time

[chiwen1]

Homework Statement

A particle rotates counterclockwise in a circle of radius 4.4 m with a constant angular speed of 11 rad/s. At t = 0, the particle has an x coordinate of 2.9 m and y > 0. Determine the x coordinate of the particle at t = 1.22 s.

Homework Equations

x = Acos(ωt + φ)

The Attempt at a Solution

Find φ, which is: cos^-1(x/A)-ωt = cos^-1(2.9/4.4) = 0.85,
then x= (4.4)cos(11(1.22)+0.85) = -0.58, which is not correct. What am I doing wrong?

 

[gneill]

Homework Statement

A particle rotates counterclockwise in a circle of radius 4.4 m with a constant angular speed of 11 rad/s. At t = 0, the particle has an x coordinate of 2.9 m and y > 0. Determine the x coordinate of the particle at t = 1.22 s.

Homework Equations

x = Acos(ωt + φ)

The Attempt at a Solution

Find φ, which is: cos^-1(x/A)-ωt = cos^-1(2.9/4.4) = 0.85,
then x= (4.4)cos(11(1.22)+0.85) = -0.58, which is not correct. What am I doing wrong?

Your method looks okay. Perhaps you're not supplying the correct precision for the answer. Keep extra decimal places in all intermediate results and only round the result at the end.