# Will the car hit the barrier?

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

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.

hage567
Homework Helper
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.