# Tangential and radial acceleration

1. Feb 28, 2007

### Why-not2007

1. The problem statement, all variables and given/known data
A particle moves in the xy plane in a circle centered origin. At a certain instant the velocity and acceleration of the particle are 4.6j m/s and (2.3i - 2.1j) m/s^2. What are the x and y coordinates of the particle at this moment

2. Relevant equations
ar=-v^2/r

3. The attempt at a solution
I took the magnitude of the radial acceleration and got 3.11 m/s^2 and plugged it into the equation. I got -6.8 for my radius and was told that was the wrong answer for the x coordinate. Then I tried plugging in 2.3 for the radial acceleration and got -9.2 for my radius. Does the -2.1j m/s^2 not play a factor in this problem? I got x=-9.2, but I don't know how to solve for the y component of the problem.

2. Feb 28, 2007

### Staff: Mentor

How did you get this? Are you assuming that the particle is moving with a constant speed? (You are given the total acceleration, not the radial acceleration.)
The velocity should tell you the y-coordinate, since it moves in a circle.

3. Feb 28, 2007

### PhanthomJay

The velocity is given as being in the 'j' direction only. That should give you a hint on the possible location of the y coordinate. Your value of the centripetal acceleration that you must use depends on the value of the y coordinate you must find first.

4. Feb 28, 2007

### Why-not2007

The y coordinate equal 0?

5. Feb 28, 2007

### Staff: Mentor

Absolutely. That's the only way to make sense of the given velocity, since that velocity must be tangential to the circle at all times.

6. Feb 28, 2007

### Why-not2007

Thanks, I appreciate the help.

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