A student tools along in his new Vette weaving in and out of slow traffic, overtaking little kids boarding the school bus, passing school zones without a second glance, cutting off ambulances and fire trucks, running yellow lights, red lights, yield signs, and stop signs invincible and uncaring in her youth. Suddenly she sees a police car 400 meters ahead. She immediately slams on her brakes and decelerates at -3.5 m/s2 and comes to a complete stop right beside the cop car. She waves and offers the officer a drink from her six-pack. OOPS. The officer shoots the student with a Taser gun and drags the student to jail for truancy.

Question

A student tools along in his new Vette weaving in and out of slow traffic, overtaking little kids boarding the school bus, passing school zones without a second glance, cutting off ambulances and fire trucks, running yellow lights, red lights, yield signs, and stop signs invincible and uncaring in her youth. Suddenly she sees a police car 400 meters ahead. She immediately slams on her brakes and decelerates at -3.5 m/s2 and comes to a complete stop right beside the cop car. She waves and offers the officer a drink from her six-pack. OOPS. The officer shoots the student with a Taser gun and drags the student to jail for truancy.
WHAT WAS THE INITIAL VELOCITY OF THE STUDENT'S CAR just prior to applying the brakes?

I don't know what equations to use... I feel like I am given a very little data to begin with, I don't even know where to start.

bobpursley · Answer

vf^2=vi^2+2ad d=400, a is given, vf=0, solve for vi