Kinematics problem help

  • Thread starter nblu
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  • #1
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Q: The average alcohol-free driver requires about 0.8 s to apply the brakes
after seeing an emergency. Calculate the distance travelled after seeing the emergency
before applying the brakes.

with the question, the given speed is 17 m/s and t = 0.8.
at first, i used d =vt equation to find the distance, however,
when i read through the question again, i had a feeling that it's not right.
my first answer was d=14m, but it just doesnt look correct.

i was thinking of finding the acceleration then use v[tex]^{2}_{f}[/tex]=v[tex]^{2}_{i}[/tex] +2a[tex]\Delta[/tex]d
to solve for d, OR, use this equation, [tex]\Delta[/tex]d=1/2(v[tex]_{1}[/tex]+v[tex]_{2}[/tex])[tex]\Delta[/tex]t, without
even having to find the acceleration.

one part of my knowledge tells me that i don't need acceleration to do this question
because this is about "before" applying the break.

its confusing me..

any help would be greatly appreciated.

thank you
 
Last edited:

Answers and Replies

  • #2
Dick
Science Advisor
Homework Helper
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You "know" what you did is right. Resist the temptation to complicate it. I'm sure you'll get a chance to use that other stuff later.
 
  • #3
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with the question, the given speed is 17 m/s and t = 0.8.
at first, i used d =vt equation to find the distance, however,
when i read through the question again, i had a feeling that it's not right.
my first answer was d=14m, but it just doesnt look correct.

one part of my knowledge tells me that i don't need acceleration to do this question
because this is about "before" applying the break.
If Dick's reply isn't enough, your logic is right to me, simple enough. I don't see how it doesn't "look correct".
 
  • #4
56
0
You "know" what you did is right. Resist the temptation to complicate it. I'm sure you'll get a chance to use that other stuff later.
If Dick's reply isn't enough, your logic is right to me, simple enough. I don't see how it doesn't "look correct".
Thank you, I really appreciate it! :)
 

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