physics As

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The table below shows how the braking distance x for a car depends on its initial speed u
u / ms-1 5.0 10 20 4
x / m 2.0 8.0 32 128
the reaction time of a driver is 0.60s. Calculate the sopping distance of the car when u= 30ms-1.

The mark scheme says:
Thinking distance= 30 X 0.6 =18m which I understand fully.
BRAKING DISTANCE =0.08 * U^2= 0.08 * 30^2= 72m IS THE BIT I DON’T UNDERSTAND. CAN SOMEONE PLEASE EXPALIN THE BRAKING DISTANCE STAGE AND WHY AND HOW YOU DO THIS BIT AS WELL AS ALL EQUATIONS INVOLVED!
Stopping distance= 18 +72= 90m which I understand fully.

please help.

Explain the working out of the braking distance for this question.

As physics - cylinder Thursday, November 9, 2017 at 7:37am
I wrote what I do know and the caps lock is what I dont know, and that is the working out for braking distance shown above is confusing to me.

As physics - Damon Thursday, November 9, 2017 at 8:39am
your table makes no sense to me

v = Vi + a t where t is AFTER 0.6 s
v = 30 + a t
so
x = Xi + Vi t + (1/2) a t^2

a will be negative of course
Xi is 18 when t = 0
x = 18 + 30 t + (1/2) a t^2

remember total stopping time = t + .6

As physics - cylinder Thursday, November 9, 2017 at 9:27am
I am in as and we dont use those symbols so im confused


Sorry for the repost i didnt understand and i just wanted to show how the working and answer went so someone can better help me


I had this question too and didnt understand it either when i went through thisquestionin a level we dont usae Xi or any of those please write in ful lsentencs ad clearly explai

  • physics As -

    What i think
    s dunno
    u 30
    v dunno
    a 9.81
    t dunno

    someone used the equation v=u+at and s=ut+1/2at^2

    if t is zero then i think v is 30 after putting the numbers in. then.. oim confused using suvat and where the numbers came from please help

  • physics As -

    Please help i hvae been confused on this for ages

  • physics As -

    You have not posted all the information needed.
    9.81 is the acceleration of gravity which has nothing to do with this. Why is there a 4 above 128?
    Please post the complete problem you were given as given.
    if acceleration and force is constant
    (1/2) v^2 = F d
    or initial kinetic energy = work done by F

  • physics As -

    Q11.The table below shows how the braking distance x for a car depends on its initial speed u.

    | u / ms-1 | 5 | 10 | 20 | 40 |
    | X / M | 2 | 8 | 32 | 128 |

    The relationship between x and u is: doubling speed increases distance by a factor of 4.

    i)The reaction time of a driver is 0.60s. Calculate the stopping distance of the car when u is 30ms-1.
    Thinking distance= 18m

    and i didntknow how to work out braking distance so i looked at the mark scheme to get this number
    so braking distance=72m
    then i used this number to get the stoppign distance and got:
    stopping idstamce=

    18m + 72m = 90m stopping distance.

    Please show mehow to work out braking distance for this questions, show where you got numbersfrom, what equations used and full wqriting not jut symbols please/

  • physics As -

    by the wa for the table
    5 is above 2
    10 is above 8
    andso on
    the space i leftr arent posted/shown

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