One way to do this: Before she reacts she continues a distance d1 with her initial velocity for the duration of her reaction time: see Ch 2 Sheet 14 for the expression for d1. What is the acceleration during this part of her travel ? When you have d1 get the remaining distance d2 she has available. During the 2nd part of her travel
she has to stop after she has traveled d2. See Sheet 15 and get the distance traveled while decelerating. Do you have all input variables to calculate the stopping distance (x-x0) ? What is your criterion when judging whether she can stop ?
4 comments:
Ok, I am not understanding this AT ALL! I tried applying the equation V^2= Vo^2+2a(X-Xo) and I put in 0 as the value for Vo and the width of the patch of ice as 5.2m, but it's not working. Help, please!
Re 9/3 9:44 pm:
I think you mean Ch2_2 #3, since you refer to a "patch of ice". If yes, show me your calculation.
If you really refer to Ch2_3 #1 get started using the blog hints.
Show me your calculation. Don't tell me in prose what you did.
Okay, so here's what I did according to the hint given. I know I probably won't see a response before the deadline, but if someone could please tell me whether my calculations are correct, I'd appreciate it, as I'll be checking back here for future reference. It's good to know how to do these things..not just get the right answer. Thanks.
To get d1:
x=x0 + v0 * t + 1/2 * a * t^2
= 0 + 20m/s * .5s + 1/2 * 0 * .5s^2
=20 * .5 + 1/2
x=10.5m
so d1 = 10.5m
Then, to get d2:
deltaX = v0 * t + 1/2 * a * t^2
= 20 * .5s + 1/2 (-6) * .5^2
= 10 + -.75
deltaX = 9.25
So d2 = 9.25
(I made the 6 m/s negative since it's deceleration)
Then d1 + d2, is it greater or less than D, the total distance to the obstacle?
d1 + d2
= 10.5 + 9.25
= 19.75
19.75 < 50m, so yes, she would stop in time.
Okay guys....I got the "yes" part correct, but I don't know if my calculations to get there were any good. Please let me know!!
@ Cahryn
From what I can see, I see 2 errors, 1 minor and 1 major. The 1 minor error is a calculation error in d1.
"= 0 + 20m/s * .5s + 1/2 * 0 * .5s^2
=20 * .5 + 1/2"
1/2*0*.5s^2 is 0, not 1/2.
The 2nd error is in your d2 calculation. For the time variable, you decided to use .5 seconds. But if you look at the question, the car is not decelerating for .5 seconds. The .5 seconds represents her reaction time.
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