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AP Physics C Kinematics Homework? - September 2nd 2010, 09:51 PM

There are two questions from my homework that I haven't figured out what to do for.

1. A driver has a reaction time of 0.50s, and the maximum deceleration of her car is 6.0m/s^2. She is driving at 20 m/s when suddenly she sees and obstacle in the road 50m in front of her. Can she stop the car in time to avoid a collision?

2. You are driving to the grocery store at 20m/s. You are 110m from an intersection when the traffi light turns red. Assume that your reaction time is 0.50s and that your car breaks with constant acceleration.
a) How far are you from the intersection when you begin to apply the breaks?
b) What acceleration will bring you to rest right at the intersection?
c) How long does it take you to stop after the light turns red?

I've tried everything. Integrals, basic kinematics equations... I've got nothing.


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Re: AP Physics C Kinematics Homework? - September 2nd 2010, 10:24 PM

Ahhh high school physics
I'll do the first and the second one just use the same steps

Ok so you know
d=v*t
d=20m/s*0.5s= 10m
Let's work now with the velocity since that's all you have
v=at
v=20m/s
a=6.0m/s^2
20m/s= 6.0m/s^2*T
T=20/6= 33.33 seconds
D= 0.5* 6.0 * 3.33^2 = 33.26 meters
And she survived and stopped before the collision.


Edit
My bad for 2 you need more

in a) use D=vt
b) Vf^2= vi^2 + 2ad
c) A= vf - vi /Δt


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Last edited by Pelios; September 2nd 2010 at 10:49 PM.
   
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Re: AP Physics C Kinematics Homework? - September 2nd 2010, 10:41 PM

YOU ARE MY NEW BEST FRIEND.


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Re: AP Physics C Kinematics Homework? - September 2nd 2010, 10:54 PM

Lol cool
In number 2 use
a) use D=vt
b) Vf^2= vi^2 + 2ad
c) A= vf - vi /Δt
vf is 0


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