# Homework Help: Circular Motion with Tension and Finding Angle

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1. Sep 17, 2015

### Physkat

1. The problem statement, all variables and given/known data
A 0.020-kg mass is attached to a 1.2-m string and moves in a horizontal circle with a constant speed. The tension in the string is measured at 0.200 N. What is the measure of angle θ?

2. Relevant equations
∑F=ma, a=v^2/r

3. The attempt at a solution
I broke down the forces at work, being T (tension) and W (weight). I made a free body diagram, then drew a graph. I came up with the x components as -Tsinθ=ma, and y components as Tcosθ-W=0. After plugging in for T and m*g (from W) in the y component equation, I came up with θ=11.2, but this is not correct.

2. Sep 17, 2015

### haruspex

The question as posted does not indicate whether the angle is to be measured from vertical or from horizontal. I assume there is some diagram which makes it clear it is to the vertical.

3. Sep 17, 2015

### Physkat

Haruspex,
Thank you for your response. Here is the image associated with the problem.

4. Sep 17, 2015

### haruspex

Then I see only four possibilities:
- you were expected to use a slightly different value of g; the answer will be somewhat sensitive to this, .980 giving 11.5 degrees e.g.
- for the same reason, you should only specify two sig figs.