Maximum Velocity for collision given acceleration

[Tearsandrille]

Homework Statement

You are driving a car going 30.0m/s; suddenly you see a scary monster 130.0 m ahead. It takes you 0.150s to react before applying the brakes, and the average acceleration during the breaking is 3.50m/s^2.
a. Determine if you hit the monster?

b. What maximum speed could you travel and not hit the monster?

Homework Equations

v = d/t
d = Vi*t + 1/2*a*t^2
Vf^2 = Vi^2 + 2*a*d

The Attempt at a Solution

I know that d1 (my reaction time distance) and d2 (my braking distance) must equal 130.0m.
I tried setting it up this way, but then I have two variables:
130m = Vi*0.150s + Vi*t + 1/2*(-3.50m/s^2)*t^2

It seems everything I try to set up is giving me two unknown variables!

Thanks in advance for help,
TS

 

[tiny-tim]

Hi Tearsandrille!

(try using the X² icon just above the Reply box )

d = Vi*t + 1/2*a*t^2
Vf^2 = Vi^2 + 2*a*d
…
It seems everything I try to set up is giving me two unknown variables!

That's because you introduced an unasked-for variable (t) …

try using your other equation! ​