Kinematics Initial Velocity problem

[andycampbell1]

Homework Statement

A deer jumped out at 40 m in front of a car traveling at 30 mph. If the car managed to stop with 10 m to spare. Determine the velocity at which the car would be traveling so that the collision could not be avoided.

Homework Equations

V_f²=V_i²+2*AD

V_f=V_i+At

S= V_i+0.5*A*t²

The Attempt at a Solution

I have been given a past paper to prepare for an exam. I have the answers which are 3.0 m/s² for acceleration and the initial velocity =15.49 m/s

I would like some help to work out the initial velocity

I have worked out the acceleration using V_f²=V_i²+2*A*D

V_f=0, V_i=13.41 m/s , D= 30 m

0²=13.41²+2A*30
0²=179.83+2A*30
A= 179,83 / 2*30 = 2.99997 or 3 m/s²

I am wondering do I need to rearrange the equation I have used above to find out the initial velocity or would it be a different equation. Also would I change the displacement to 40 m

Thanks

 

[PhanthomJay]

Same equation, same acceleration, and yes, change displacement to 40 m and solve for the initial velocity.