# physics

A car leaves skid marks 90 long on the highway in coming to a stop.

Assuming a deceleration of 3.5m/s^2, estimate the speed of the car just before braking.

1. 👍 0
2. 👎 0
3. 👁 253
1. 0 = Vi - a t
so
t = Vi/3.5

d = Vi t - (1/2)(3.5) t^2
90 = Vi^2/3.5 - 1.75 Vi^2/12.25

Vi^2 - .5 Vi - 315 = 0

Vi = [ .5 +/- sqrt ( .25 + 1260) ]/2

Vi = [ .5 +/- 35.5 ] / 2

Vi = 18 m/s

1. 👍 0
2. 👎 0
posted by Damon
2. 15

1. 👍 0
2. 👎 0

## Similar Questions

1. ### physics

In coming to a stop, a car leaves skid marks 77 long on the highway Assuming a deceleration of 7.20 , estimate the speed of the car just before braking

asked by Anonymous on September 11, 2012
2. ### Physics 1

In coming to a stop, a car leaves skid marks 62 m long on the highway.Assuming a deceleration of 4.30 m/s2 , estimate the speed of the car just before braking.

asked by Anonymous on January 23, 2017
3. ### Physics

In coming to a stop, a car leaves skid marks 88 m long on the highway. Assuming a deceleration of 7.50 m/s2, estimate the speed of the car just before braking.

asked by Carlee on August 30, 2012
4. ### physics

In coming to a stop, a car leaves skid marks 77 long on the highway Assuming a deceleration of 7.20 , estimate the speed of the car just before braking

asked by Anonymous on September 11, 2012
5. ### Physics

In coming to a stop, a car leaves skid marks 97.0 m long on the highway. Assuming a deceleration of 6.60 m/s2, estimate the speed of the car just before braking. (in m/s)

6. ### physics 1

In coming to a stop a car leaves skid marks 92m long on the highway. Assuming a decceleration of 7.00m/s^2, estimate the speed of the car just before braking.

asked by john on September 13, 2010
7. ### Physics Part A HELP!!

4.) In coming to a stop, a car leaves skid marks 80m long on the highway. Assuming a DEceleration of 7.00 m/s^2 (m/s/s), estimate the speed of the car just before breaking. 6.) A car traveling @ 90km/h strikes a tree. The front

asked by Jess on December 14, 2015
8. ### Physics

a car leaves skid marks 84 m long on the highway. Assuming a deceleration of 7.50 m/s2, estimate the speed of the car just before braking.

asked by Shay on September 19, 2011
9. ### Physics

Police find skid marks 66 m long on the highway showing where the car made an emergency stop. Assuming that the acceleration was -10 m/s2 (about the maximum for dry pavement), how fast was the car going?

asked by Katie on September 5, 2011
10. ### Physics

Police find skid marks 65.0 m long on a highway showing where the car made an emergency stop. Assuming the acceleration was -10.3 m/s^ ( about the maximum for dry pavement) how fast was the car going?

asked by Tyler on September 19, 2015

More Similar Questions