# Constant Acceleration; answer not correct for some reason?

1. Jan 27, 2014

### dudenamedscott

1. The problem statement, all variables and given/known data
A motorist suddenly notices a stalled car and slams on the brakes, negatively accelerating at 6.1m/s2 . Unfortunately this isn't enough, and a collision ensues. From the damage sustained, police estimate that the car was going 22km/h at the time of the collision. They also measure skid marks 35m long. Aow fast was the motorist going when the brakes were first applied? B: How much time elapsed from the initial braking to the collision?

2. Relevant equations
2 a (x - xo)= v2 - vo2
v(average)=d/t

3. The attempt at a solution
A: 2(6.1m/s^2)(35-0m)=(55/9m/s)^2-vo^2
vo^2=19.7m/s

B: 19.7m/s=35/t
t=1.78sec

I may just be totally off, but I feel like I understood the problem. Masteringphysics doesn't agree. Thanks again haha.

2. Jan 27, 2014

### lightgrav

you mean v = 19.7 m/s ? ... are acceleration and displacement in the same direction?