# Centripetal acceleration problem (very easy)

1. Jul 17, 2007

### coding_delight

A 2.5 kg object moves at a constant speed of 8.0 m/s in a 5.0 m radius circle. What is the object's acceleration?

I'm quite sure the answer to the problem is 32 m/s^2, but apparently the right answer is 13 m/s^2. Unless I'm missing a detail about the "constant velocity" part of the problem, can some one please explain why the answer is 13.

2. Jul 17, 2007

### Danger

Welcome to PF, Coding... but you're in the wrong forum. This is pretty obviously a homework question, which is not allowed in this section. As such, you must show what you've already done by way of figuring it out.

3. Jul 17, 2007

### bel

$$a_c= \frac{v^2}{r}$$

The mass is superfluous.

4. Jul 18, 2007

### HallsofIvy

Staff Emeritus
How could you possibly have got "32 m/s^2"? The only way to combine the numbers given to get 32 would be "82 times 2.5 divided by 5". If you do that, your units would be kg m/s2, not m/s2. Since there is no mass unit in acceleration, as bel says, the mass is irrelevant.

5. Jul 18, 2007

### ank_gl

duh.. 32 units is the force, 13units is the acceleration

6. Oct 14, 2009

### rsamudrala

acceleration = v*v/r
= 8*8/5
= 64/5=12.8
= 13 (approx)