# Homework Help: Help me with this uniform accelration problem

1. May 31, 2007

### Tehy

I'm learning physics and I'm now working on with one line motion problems and I'm jammed with this one problem:

A ball starts from rest and rolls down a hill with uniform accelration, traveling 150m during the second 5.0s of it's motion. How far did it roll during the first 5.0s of motion?

I just can't figure out how to solve this. Could someone help me?

Thanks!

2. May 31, 2007

### prasannapakkiam

This sounds like a homework question.

Anyway:
http://www.physchem.co.za/Graphs/Equations.htm [Broken]
The 4 Basic linear Equations of Motion can help.

Hint:
-Use s=ut+(at^2)/2 & v=u+at
-Find a
Then use s=ut+(at^2)/2

If you need more help post at the Homework Questions section.

Last edited by a moderator: May 2, 2017
3. May 31, 2007

### Tehy

Yeah, I have tried those equations, but I can't get the right answer...

Last edited: May 31, 2007
4. May 31, 2007

### arunbg

Please post how you worked out the problem, so that we may point out the errors.

5. May 31, 2007

### Tehy

Well, I'll try :) So ball starts from rest, so Xo = 0, Vox = 0, T1 = 0. Then the ball rolls 5s and it's place is X1 and V1x = ?. Finally the ball rolls the second 5s and then X2 = X1 + 150m, V2x = ? and T2 = 10s

When the ball rolls first 5s:
(1) X1 = 1/2(AxT1^2)

The ball rolls second 5s (from X1 to X2):
(2) X2 = X1 + V1xt + 1/2(AxT2^2)

Then I combine those equations (1) and (2), but with no luck.

6. May 31, 2007

### arunbg

You should also write V1 in terms of the acceleration A.
Eliminate all other unknowns except A, remember you have values for X2, T1 and T2.

7. May 31, 2007

### prasannapakkiam

Correct me if I may be wrong.

df=distance in first 5s
t=5 in all cases

df=ut+(at^2)/2
since: v=u+at
therefore:df=(0+at)t+(25a)/2
therefore:150=37.5a

Last edited by a moderator: May 31, 2007
8. Jun 1, 2007

### arunbg

Yes, you are correct and I hope the OP has understood the solution.