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Kinematics Homework Help (2D motion)-Stopping over time

  • #1

Homework Statement



You're driving down the highway late one night at 18m/s when a deer steps onto the road 41m in front of you. Your reaction time before stepping on the brakes is 0.5s and the maximum deceleration of your car is 12 m/s/s

Homework Equations



1) How much distance is between you and the deer when you come to a stop?
2) What is the maximum speed you could have and still not hit the deer?

The Attempt at a Solution



Am I doing this right? She gives us the answer of 19m for the 1st question and 25m/s for the 2nd question. But I am coming up with a different answer for the first question.

First I figured the distance between the car and deer to be 36m, after you take into account the 0.5s reaction time. Then I started to calculate distance it takes to stop.

The equation I used was vf2 = vo2+2*a*d

I plugged in the variables to get 0m2/s2 = 324m2/s2 + (-24m2/s2)*d ... I solve for d to get 13.5m, which is the distance traveled. Take 36m - 13.5m to get 22.5m from the deer, not 19m. I have not attempted the 2nd question yet because I thought I may be doing something incorrect.
 

Answers and Replies

  • #2
662
307
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First I figured the distance between the car and deer to be 36m, after you take into account the 0.5s reaction time. Then I started to calculate distance it takes to stop.
.
That should be 32.
 

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