- #1
Abdul.119
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Homework Statement
A car starts from rest at a stop sign. It accelerates at 3.7m/s^2 for 7.3s , coasts for 1.6s , and then slows down at a rate of 3.3m/s^2 for the next stop sign.
How far apart are the stop signs?
Homework Equations
d = vt +1/2 a*t^2
Vf = Vi + a*t
Vf^2 = Vi^2 + 2a*s
The Attempt at a Solution
I believe I should calculate the distance over the first 7.3 seconds, which would be 1/2*3.7*(7.3^2) = 98.6 m.. ok when it coasts for 1.6s, I think we must assume there is no friction? so the velocity from there is Vf^2 = 0 + 2*3.7*98.6, Vf = 27m/s, traveling at that speed for 1.6s would travel 43.216 meters.. now I'm not sure how to find the distance traveled in the last part, but I know it took the car 27/3.3 = 8.1 seconds to decelerate from 27 m/s to 0 m/s .. how do I find that last distance? I tried the first equation which gave me 110.5 meters.. is that correct? and the total distance from the two stop signs would be 252 m? (I don't want to put a wrong answer because it gets penalty)
Thanks