
#1
Dec3008, 06:38 AM

P: 6

1. The problem statement, all variables and given/known data Hi all, the question for revision is; A car of mass 600kg travelling at 45m/s comes to rest in 12m when the brakes are applied. What is the average force exerted by the brakes?
2. Relevant equations Force = mass x acceleration V^2=u^2 +2as 3. The attempt at a solution I know I need to work out the acceleration but am having trouble correctly transposing that equation I think its this v^2u^2 divided by s =2a, its what to do with the 2 to get a on its own, does it then become 1/2 s on the other side? 



#2
Dec3008, 07:27 AM

Mentor
P: 11,988

Let's write out what you correctly have so far: [tex] \frac{v^2u^2}{s}=2a [/tex] Hopefully that helps you see better what to do ... if not, then post again. p.s. I'm not quite sure if 



#3
Dec3008, 07:47 AM

P: 6

That is what i have so far, Im just not sure where the 2 goes so you just get a on its own, I was wondering the 2 then moves to the side of s to become1/2s.




#4
Dec3008, 07:53 AM

P: 6

Calculating acceleration and brake force
If I solve that equation with 2a. I did the following 45x450x0, divided by 12 = 168.75 x 2 =337.5. Is this the correct acceleration?




#5
Dec3008, 08:00 AM

P: 3,012

[tex]\frac{v^2u^2}{s}=2a[/tex]
[tex]\Rightarrow \frac{v^2u^2}{2s}=a[/tex] 



#6
Dec3008, 08:15 AM

P: 6

Yes I have it, thank you, my transposition of equations knowledge is in there, but its 15 years or so since I used it! I often write the suvat list out, i find it very helpful.



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