Physics Questin HELP

[aiyla]

i need help with this question... its from my text book and there isn't any answers  at the back of the text book.

1. A car is traveling along a road at 30m/s when a pedestrian steps into the road 55m ahead. The driver of the car applies the brakes after a reaction time of 0.5s and the car slows down at a rate of 10m/s² . what happens ?


can anyone help me ? 

[nid404]

A car is traveling along a road at 30m/s when a pedestrian steps into the road 55m ahead. The driver of the car applies the brakes after a reaction time of 0.5s and the car slows down at a rate of 10m/s2 . what happens ?

Initial speed=30m/s
thinking distance=30x0.5=15m
breaking distance=30²/ (2X10)
=45m

stopping distance=60m.....

oops!!!!!! the pedestrian is knocked down by the car

[aiyla]

can u tell me about the thinking distance part ?
why didn't i think of that ? i did the question till i got 45 then i didn't know what to do any more .


so can you please tell me what you did in that part ? or why did u have to do it ?


and thanks ALOOTTDOZENTIMES

[astarmathsandphysics]

The driver has to think "I have to brake". He takes 0.5seconds to do this so using the eqaution ditance =speed*time we get the 15m

[nid404]

you calculate the thinking distance because the car travels some distance before the brakes are applied
Stopping distance=breaking distance+thinking distance
thinking distance=reaction time X initial velocity of the car
breaking distance u find by taking v2=u2 + 2 X a X s

[aiyla]

thanks alot guys =)
if only the book had the answers at the back it would have been much better =\