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

TerribleGrades
Badges: 15
Rep:
?
#1
Report Thread starter 2 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.
Attached files
0
reply
Mr M
Badges: 20
Rep:
?
#2
Report 2 years ago
#2
(Original post by TerribleGrades)
...
Use equation 2 to find acceleration and then use equation 1 to find final velocity.
0
reply
Mistletoe
Badges: 2
Rep:
?
#3
Report 2 years ago
#3
need to rearrange equation 2 to find the uniform acceleration
0
reply
Welshstig
Badges: 16
Rep:
?
#4
Report 2 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
reply
Mistletoe
Badges: 2
Rep:
?
#5
Report 2 years ago
#5
(Original post by Welshstig)
I'll get you started, final velocity is just simply: total displacement / total time

Using your values:

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
reply
Benb2000
Badges: 2
Rep:
?
#6
Report 2 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
reply
Welshstig
Badges: 16
Rep:
?
#7
Report 2 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
reply
Welshstig
Badges: 16
Rep:
?
#8
Report 2 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
reply
TerribleGrades
Badges: 15
Rep:
?
#9
Report Thread starter 2 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
reply
Benb2000
Badges: 2
Rep:
?
#10
Report 2 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
reply
Sir Cumference
  • Study Helper
Badges: 20
Rep:
?
#11
Report 2 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.

s=ut+\frac{1}{2}at^2

Plug in s=40, u=0 and t=12 then see if you can work out a from there.
0
reply
Welshstig
Badges: 16
Rep:
?
#12
Report 2 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
reply
baiichi
Badges: 7
Rep:
?
#13
Report 2 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
reply
TerribleGrades
Badges: 15
Rep:
?
#14
Report Thread starter 2 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
reply
Vikingninja
Badges: 21
Rep:
?
#15
Report 2 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.
1
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

University open days

  • University of Bristol
    Undergraduate Open Afternoon Undergraduate
    Wed, 23 Oct '19
  • University of Exeter
    Undergraduate Open Day - Penryn Campus Undergraduate
    Wed, 23 Oct '19
  • University of Nottingham
    Mini Open Day Undergraduate
    Wed, 23 Oct '19

Have you made up your mind on your five uni choices?

Yes I know where I'm applying (158)
59.18%
No I haven't decided yet (63)
23.6%
Yes but I might change my mind (46)
17.23%

Watched Threads

View All