What is the car's acceleration while braking?

Question

A car accelerates uniformly from rest at 12.5 m/s^2 for 10 seconds. It then brakes to a rest over a distance of 1000 meters.

Answer 1

Distance= distance while accelerating + distance while braking

 

distance while accelerating= 1/2*a*t²=1/2 *12.5*100=625m

 

=>

1000m=625m+distance while braking

 

=>

 

distance while braking is 1000-625=375m

 

distance=( 0-V_i²) /2a  => a=-V_i² /2*distance 

 

V_i while braking= V_f while accelerating= a* t= 12.5*10=125

 

=>

 

a=-(125)²/(2*375)= -20.83 m/s²