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## Homework Statement

A girl swings a 2.7kg ball attached to a 72.0-cm string in a horizontal circle above her head, which makes one revolution in .98s. What is the tension force, [tex]F_{T}[/tex], exerted on the string by the ball?

## Homework Equations

Alright, I have never worked with Tension Force in my class, but we have worked with basic physic formulas, which I applied to this problem. Since mass and time are given, I assumed to use Displacement & Time (assuming 72cm [or 0.72m] is displacement instead of radius, since I'm unsure if it's radius or not...), which is:

[tex]x = x_0 + v_0 t + (1/2) a t^2[/tex]

For the second part, I applied Newton's Second Law to find Tension Force.

[tex]{F} = {m}{a}[/tex]

## The Attempt at a Solution

[tex]x = x_0 + v_0 t + (1/2) a t^2[/tex]

or (assuming [tex]v_0[/tex] is 0):

0.72 = (1/2) (a) (0.98)^2

And for acceleration I got [tex]1.49 (m/s)^2[/tex].

Then, applying Newton's Second Law:

[tex]{F} = {m}{a}[/tex]

or

F = (2.7)(1.49) = 4.04 N.

However, my only available answers are 3.8N, 3*(10^3)N, 8*(10^1)N, and 92N.

I would of rounded 4.04N to 3.8N and moved on, but I have a strong feeling I did this entire problem wrong.

If I did, could someone explain what I did wrong and guide me in the right direction?

Thanks!

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