# Acceleration question

1. Oct 21, 2006

### petal5

I've been attempting the following question:

A 120gram hockey puck sent sliding over ice with an initial speed of 5.5m/s is stopped in 15m by the frictional force on it from the ice.What is the acceleration experienced by the puck?

I'm getting an answer of 2.0157m/s^2.I'm wondering if this is correct or not?
Thanks.

2. Oct 21, 2006

### Hootenanny

Staff Emeritus
If you assume the acceleration is constant then your answer is incorrect. Perhaps if you show your working we could correct you. Also note that the acceleration should be negative since the puck's velocity is decreasing.

3. Oct 21, 2006

### petal5

i used the formula vf-vi/tf-ti to get that answer

4. Oct 21, 2006

### Hootenanny

Staff Emeritus
And how did you calculate the time?

5. Oct 21, 2006

### petal5

i divided 15m by 5.5m.however,i now realise this is wrong as the 5.5m. is INITIAL speed

6. Oct 21, 2006

### Hootenanny

Staff Emeritus
Indeed, so if we assume the acceleration to be uniform how does the displacement, initial and final velocity relate to the acceleration?

7. Oct 21, 2006

### petal5

sorry,i've no idea.

8. Oct 21, 2006

### Hootenanny

Staff Emeritus
Last edited by a moderator: Apr 22, 2017
9. Oct 21, 2006

### petal5

would it be this equation:v^2=vo^2+2a(x-xo)

10. Oct 21, 2006

### Hootenanny

Staff Emeritus
Indeed it would, all that is left to do is some algebraic manipulation and to substitute in your values.

11. Oct 21, 2006

### petal5

thanks for all your help.i'm now getting -1.01m/s^2

12. Oct 21, 2006

### Hootenanny

Staff Emeritus
Looks about right to me. My pleasure.

13. Oct 21, 2006

### petal5

Thanks so much,you're a great teacher!

14. Oct 21, 2006

### Hootenanny

Staff Emeritus
Thank you very much I do my best.