# Homework Help: SUVAT and a Constant

1. Jul 23, 2017

### thejosh

1. The problem statement, all variables and given/known data
A vehicle Accelerates from rest (a) and travels a certain distance s1 It then deccelerates (a) at a constant rate and travels a second distance s2 until it stops. If s2/s1 = K then what is the accleration (a) of the vehicle.

2. Relevant equations
v=u+at
s=ut+1/2at^2
s=vt-1/2at^2
v^2=u^2 + 2as
s=(u+v)t/2

3. The attempt at a solution
I used v^2=u^2 + 2as to describe the two parts of the journey but I ended up at a completely incorrect answer.

2. Jul 23, 2017

### willem2

There is a problem her, You have a for both the accelaration and the deceleration, but if they are the same, you would need s1=s2, and the acceleration is can still be anything. Are you sure this is correct?

3. Jul 23, 2017

### thejosh

Sorry, you are actually supposed to make an expression for K using a as the link between the two parts of the journey.

4. Jul 23, 2017

### willem2

There still seems to be missing something. Are the times of the acceleration and deceleration equal?

5. Jul 23, 2017

### haruspex

The question does not make sense as it stands. I suggest that there are two different magnitudes of acceleration, and you are supposed to find one of them in terms of K and the other acceleration.

6. Jul 24, 2017

### thejosh

You are supposed to find an expression by describing the two parts of the journey using suvat equations in terms of K the constant, the link IS a which is why they are the same, I tried using the suvat equation v^2=u^2+2as as there is no time in the equation it is just the linking and final conclusions that I struggled with.

7. Jul 24, 2017

### thejosh

You are supposed to find an expression by describing the two parts of the journey using suvat equations in terms of K the constant, the link IS a which is why they are the same, I tried using the suvat equation v^2=u^2+2as as there is no time in the equation it is just the linking and final conclusions that I struggled with.

8. Jul 24, 2017

### Staff: Mentor

As others have pointed out, the magnitudes of the acceleration and deceleration cannot be the same except for the trivial case where s1 = s2.

So did you mean to write "a" for both accelerations?

9. Jul 24, 2017

### haruspex

Suppose, for example, that K=1. If it accelerates at a for distance s1=s it reaches speed v where v2=2as. If it now decelerates at a for s2=s it will come to a stop. Thus, we have met the conditions, yet a is anything at all.
Are you quite sure you have written out the question exactly as given to you, down to the last dot and comma?

10. Jul 29, 2017

### thejosh

Thanks guys I solved it and as haruspex clearly pointed out I did not read the question carefully neither did I type it out correctly I am seriously sorry but I appreciate the help all the same, I just ran out of wifi for a while.