# I don't get SUVAT equations at all...

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Thread starter 3 years ago
#1
Basically we've been told to use one of those four equations.

To answer these questions:
1. A car accelerates uniformly from rest and after 12 seconds has covered 40m. What are its acceleration and its final velocity?
S - 40m
U - 0 m/s
V - ?
A - ?
T - 12seconds

How can I work out the acceleration without the final velocity - V-U/T = or even the final velocity without the acceleration? :/
The fact that I have to use one of 4 possible equations frustrates me even more.
0
3 years ago
#2
(Original post by TerribleGrades)
...
Use equation 2 to find acceleration and then use equation 1 to find final velocity.
0
3 years ago
#3
need to rearrange equation 2 to find the uniform acceleration
0
3 years ago
#4
*edit* I'm an idiot

With SUVAT equations you only need 3 of 5 possible values to find ALL of the other values. If you are confused to what equations you need, you need not worry! As all you have to do is check what values you have and want to find that match up the with one of the equations.

Say for example, you have displacement, initial velocity and acceleration but want to find final velocity, you just use the equation with all four values, in this case you would have to use: v^2 = u^2 + 2as.
0
3 years ago
#5
(Original post by Welshstig)
I'll get you started, final velocity is just simply: total displacement / total time

S - displacement = 40

T - time - 12

Therefore we can deduce that the final velocity is: 40/12 = 3.33 m/s.

With SUVAT equations you only need 3 of 5 possible values to find ALL of the other values. If you are confused to what equations you need, you need not worry! As all you have to do is check what values you have and want to find that match up the with one of the equations.

Say for example, you have displacement, initial velocity and acceleration but want to find final velocity, you just use the equation with all four values, in this case you would have to use: v^2 = u^2 + 2as.
Incorrect that is the average velocity.
2
3 years ago
#6
Well for the one you have stated, where you have S, U and T given, you can look at each of your suvat equations and deduce which one you can use to find one Unknown. The second equation, s = ut + 1/2at^2, when subbed with the information given leaves you with the unknown you're looking for, a.

E.g 40 = 0xt + 1/2a(12^2)
Rearrange for 80/144 = a

So essentially you have rearranged s = ut + 1/2at^2 to s/0.5t^2 = a
0
3 years ago
#7
(Original post by Mistletoe)
Incorrect that is the average velocity.
Whoops, I think im on another planet, i'll edit that know, thanks lmao
0
3 years ago
#8
(Original post by Mr M)
No that's nonsense I'm afraid.
Yeah I have no clue why I just did that haha
1
Thread starter 3 years ago
#9
(Original post by Benb2000)
Well for the one you have stated, where you have S, U and T given, you can look at each of your suvat equations and deduce which one you can use to find one Unknown. The second equation, s = ut + 1/2at^2, when subbed with the information given leaves you with the unknown you're looking for, a.

E.g 40 = 0xt + 1/2a(12^2)
Rearrange for 80/144 = a

So essentially you have rearranged s = ut + 1/2at^2 to s/0.5t^2 = a
Im sorry but where did you get 80/144 from?
0
3 years ago
#10
(Original post by TerribleGrades)
Im sorry but where did you get 80/144 from?

40 / 1/2 = 80
Then, divide this by the t^2 (12^2) = 80/144

The 0 x t is equal to nothing, so it is just cancelled
0
3 years ago
#11
(Original post by TerribleGrades)
Im sorry but where did you get 80/144 from?
You really need to try it yourself then post your working if you get stuck.

Plug in , and then see if you can work out from there.
0
3 years ago
#12
If you don't understand the concepts of SUVAT and why they work I'd suggest looking up how to actually derive them (without calculus to make it a bit easier) just to sort of "re-assure" yourself that they do actually work (and so you don't end up like me trying to break maths in some wonderfully whacky way).
0
3 years ago
#13
I would just choose 2 and 4 tbh.

You already got S, U and T so you just need to look at equations that don't have 2 unknowns ie. 1 and 3.
So you got 2 and 4 left.

Then, all you need to do is substitute the given info into the equations to get the answers.

Since this question is pretty simple and M1 (I assumed) is pretty much making things as simplified as they could so you don't need to fret too much (I think)
0
Thread starter 3 years ago
#14
Thank you, guys! I think I'm getting the hang of it now.
1. Initial velocity 5m/s, final velocity 36km/hr, acceleration 1.25m/s^2. Time and Displacement?

S = ?
U = 5
V = 36km/hr into m/s = 10
A = 1.25m/s^2
T = ?

So to work out the time, I figured equation 1 would be best as it only had one unknown:

v = u + at

To get time on its own:
v-u / a
10-5 / 1.25 = 4s

To work out the displacement (s), I figured equation 2 or 4 would be best as they are displacement equations and I have no unknowns left anyway:

Equation 4: 0.5 x (u+v) x t
0.5 x (5+10=15) x 4 = 30
Therefore, displacement must be 30m.

0
3 years ago
#15
When I used SUVAT I wrote out each letter and put the corresponding values in with the one that the question asks you to find as ?, this helps you know which equation to use by looking at which one contains all those values.
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