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posted by  chibyke/chibyskey on 5/9/2008 9:12:46 AM  |  status: Live  

kinematics

Course Textbook Chapter Problem
General Physics introductory university physics 2 21
Question Details:
a car driver travelling at a speed of 15.0m/s, see the red on a traffic light and applies his brakes. the brake was applied 0.65secs after he saw the light. if the car decelerates at 7.5 metres per squared seconds after the brake has been applied, what is the total distance travelled by the car from the point which he seaw the light.

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posted by LAPHROAIG on 5/9/2008 9:32:39 AM  |  status: Live
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chibyke/chibyskey's comment:
"thanks a lot"
Response Details:
First the car travels Δx=(15m/s)(.65s)= 9.75meters, and V2-Vo2=2aΔx and V=0, so we should have Δx= -Vo2/(2a)=-(15)2/(2(-7.5))= 15 meters, so the total distance traveled is 15+9.75= 24.75 meters
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posted by Bonga on 5/9/2008 10:45:01 AM  |  status: Live
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Response Details:
take +ve direction torwards the traffic light.
∴ distance travelled before driver applies brakes
distance travelled after appliying brakes()
=
∴-225=-15s
∴s=15m
∴total s=15m+9.75m=24.75m
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