An automobile is traveling at 90 km/h (25 m/s) on a narrow country road when the

Question

An automobile is traveling at 90 km/h (25 m/s) on a narrow country road when the driver suddenly notices a cow on the road 30 m ahead. The driver attempts to brake the automobile, but the distance is too short. Assume that the reaction time of driver is 0.75 s and that the deceleration of the automobile is 8.0 m/s2

a. With what velocity does the automobile hit the cow?

b. Sketch the velocity-time and acceleration-times graphs for the motion of the car.

please workout the problem step by step and show any kinematic formula conversions you made.

Explanation / Answer

Traveling at 25m/s for that extra 0.75s means that there is even less distance than the 30m originally given. d = v *t
25m/s *0.75s = 18.75m so 30m - 18.75m = 11.25m

Now you can figure out the final speed. v2 = vo2 + 2ax v(25m/s)2 + 2(-8 * 18.75) = 18.02m/s The velocity time graph would have a straight sloped line down to the right from 25m/s to 18.02m/s. The acceleration time graph would have a horizontal line at -8m/s2. Hope that helps

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