# How to find the tangential velocity of an object

The centripetal force on a 0.82 kg object on the end of a 2.0 massless string being swung in a horizontal circle is 4.0 N. What is the tangential velocity of the object?

The answer I got is 3.1 m/s squared but I don't know how to show the work for it. So please help me.

 ebaines Posts: 10,589, Reputation: 5794 Expert #2 Feb 24, 2010, 03:47 PM

Combine two concepts:

1. F = ma
2. For objects in circular motion with constant tangential velocity:
a = v^2/R

So:

F = ma = mv^2/R for objects in circular motion with constant tangential velocity

You now have everything you need to deermine the value of v.
 MS_SUMTER2010 Posts: 55, Reputation: 10 Junior Member #3 Feb 24, 2010, 03:56 PM

so it will be this:

4=v sqaured/ 2
then I get 2.8.

but when I plug it back in the equation v^2/r.. I get 3.9
 Unknown008 Posts: 8,147, Reputation: 3745 Uber Member #4 Feb 25, 2010, 03:10 AM

You didn't read ebaines post well. You combine F=ma and a = v^2/r.

Then you get:

$F = \frac{mv^2}{r}$

From there, you 'll get your answer as 3.1 m/s^2 (2 sf)
 MS_SUMTER2010 Posts: 55, Reputation: 10 Junior Member #5 Feb 25, 2010, 05:51 AM
OK but what is the v squared part? Because it doesn't really say. I know the mass and the radius I just don't know how to get the velocity
 ebaines Posts: 10,589, Reputation: 5794 Expert #6 Feb 25, 2010, 07:11 AM

Starting with the formula we gave you:

$
F = \frac {m v^2} r
$

Raarrange to get $v^2$ by itself:

$
v^2 = \frac {F r} m
$

and take the square root of both sides:

$
v = \sqrt { \frac {Fr} m}
$

You have valius for $F, \ r$ and $m$, so you can solve for $v$. Your answer will in units of meters/sec (NOT meters per second squared, as you had in your original post)
 IWishICouldFly Posts: 1, Reputation: 1 New Member #7 Aug 23, 2010, 03:59 PM
Quote:
 Originally Posted by ebaines Starting with the formula we gave you: $ F = \frac {m v^2} r$ Raarrange to get $v^2$ by itself: $ v^2 = \frac {F r} m $ and take the square root of both sides: $ v = \sqrt { \frac {Fr} m}$ You have valius for $F, \ r$ and $m$, so you can solve for $v$. Your answer will in units of meters/sec (NOT meters per second squared, as you had in your original post)
Thank you so much I was looking for this

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