# Homework Help: Accelerating Ball

1. Mar 13, 2009

### ride4life

1. The problem statement, all variables and given/known data
A ball initially at rest and constantly accelerating covers a distance of 10 metres during its third second of motion. What is its acceleration?

2. Relevant equations
No idea which equations I need. I'm guessing I need
a = (v-u)/t

3. The attempt at a solution
I've got no idea how to even apporach this. I'm thinking:
s = 3 s
u = 0 m/s
v =
a =
t =

2. Mar 13, 2009

### tiny-tim

Welcome to PF!

Hi ride4life! Welcome to PF!

Hint: call the acceleration a, and find the distances after 2 seconds and after 3 seconds, and find the value of a that makes their difference equal 10 metres

3. Mar 13, 2009

### ride4life

What formula should I use to figure the distanes covered in each second?

0 - 1 = ?
1 - 2 = ?
2 - 3 = 10m = 10m/s/s

I was thinking in the 1st second it travelled 2.5m and in the 2nd second it travelled 5m. I think that turns out to be 2.5m/s/s. That's just a guess. That's all I can figure out. :(

4. Mar 13, 2009

### rl.bhat

You can use, displacement s = ut +1/2*a*t^2.
Find s for 2s and 3s. Then find the difference which is equal to 10m.

5. Mar 13, 2009

### ride4life

So for
2 - 3 = 10m

s = 10m
u = ?
a = ?
t = 1s

6. Mar 13, 2009

### rl.bhat

Ball starts from rest. So u = 0.
S2 = 1/2*a*(2)^2........(1)
S3 = 1/2*a*(3)^2........(2)
Find S3 - S2, equate it to 10m, and solve for a.

7. Mar 13, 2009

### ride4life

Thanks for the help, I got 4m/s/s which is the right answer. :D