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Will the car hit the barrier?

  • Thread starter adamlazz
  • Start date
  • #1
1
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Hi there, I am a grade 11 student, learning physics.

Homework Statement



A driver of a car going 90km/h suddenly sees the lights of a barrier 40.0 m ahead. It takes the driver 0.75s before he applies the brakes and the average accelleration during braking is -10.0m/s2.
a) Determine whether or not the car hits tha barrier.
b) What is the maximim speed at which the car could be moving and not hit the barrier at 40.0 m ahead? Assume the accelleration does not change.

a) Treat toward the barrier as positive.
v2=0m/s delta(t)= 40
v1=25m/s
a=-10m/s2

I am not quite sure how to do b)


Homework Equations



v2^2 = v1^2 + 2a(delta(d)) <---- a)

The Attempt at a Solution



I have already determined that it would take the car 50 m to come to a complete stop, so it would hit the barrier.

I am having trouble with b)


thanks in advance.
 

Answers and Replies

  • #2
8
0
I could be wrong but you just need to use the same formula again:

v2^2 = v1^2 + 2a(delta(d)) <---- a)

You know d, v2 is 0, and your given acceleration from before

There is only one unknown left, V1.
 
  • #3
hage567
Homework Helper
1,509
2
If you assume the car will stop just before it hits the barrier, you now have a new piece of information you can use in your equations to work out the new v1.
 

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