Join TSR now and get all your revision questions answeredSign up now

Which SUVAT equation do I need for this?

    • Thread Starter
    Offline

    2
    ReputationRep:
    A car is travelling at 36km/h when the driver has to perform an emergency stop. During the time the driver takes to appreciate the situation and apply the brakes the car has traveled 7m. It then pulls up with constant deceleration in a further 8m, giving a total stopping distance of 15m.

    a) Find the initial speed of the car in m/s and the time that the driver takes to react

    S=15
    U=36
    V=0
    A=A
    T=T
    Offline

    2
    ReputationRep:
    (Original post by ℓove)
    A car is travelling at 36km/h when the driver has to perform an emergency stop. During the time the driver takes to appreciate the situation and apply the brakes the car has traveled 7m. It then pulls up with constant deceleration in a further 8m, giving a total stopping distance of 15m.

    a) Find the initial speed of the car in m/s and the time that the driver takes to react

    S=15
    U=36
    V=0
    A=A
    T=T
    Convert to m/s first

    Posted from TSR Mobile
    Offline

    2
    ReputationRep:
    First part of question is converting from km/h to m/s, so 36'000m/h then divide that by 60^2 (=10m/s).
    The reaction time is the time before he applies the brakes, so it is before deceleration begins therefore aA= 0.
    So set up S = 7, U = 10, V = U (bc A = 0) A = 0 T = ?
    A good equation might be s = ut + 1/2at^2, since a is 0 and the whole second term disappears
    Offline

    3
    ReputationRep:
    (Original post by ℓove)
    A car is travelling at 36km/h when the driver has to perform an emergency stop. During the time the driver takes to appreciate the situation and apply the brakes the car has traveled 7m. It then pulls up with constant deceleration in a further 8m, giving a total stopping distance of 15m.

    a) Find the initial speed of the car in m/s and the time that the driver takes to react

    S=15
    U=36
    V=0
    A=A
    T=T
    Well the first part is just converting km/h into m/s.

    For the second one, you know that the car travels 7m before the brakes are applied, so the displacement is 7.

    You know S, U, V and A which is the majority of the variables so you can use pretty much any SUVAT equation you want but not all of them will be able to tell you the time. I'd personally go for s=\frac{1}{2}(u+v)t but if you notice shortcuts like above since a=0 then you may use that as well.
 
 
 
Poll
Which party will you be voting for in the General Election 2017?
Useful resources

Make your revision easier

Maths

Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

Equations

How to use LaTex

Writing equations the easy way

Student revising

Study habits of A* students

Top tips from students who have already aced their exams

Study Planner

Create your own Study Planner

Never miss a deadline again

Polling station sign

Thinking about a maths degree?

Chat with other maths applicants

Can you help? Study help unanswered threads

Groups associated with this forum:

View associated groups

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Quick reply
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.