IGCSE/GCSE/O & A Level/IB/University Student Forum
Qualification => Subject Doubts => GCE AS & A2 Level => Sciences => Topic started by: aiyla on October 09, 2009, 12:46:17 pm
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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 ?
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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
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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
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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
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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
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thanks alot guys =)
if only the book had the answers at the back it would have been much better =\