In coming to a stop,car leaves skid marks on highway 320m long.assume deceleration of 10m/s2,estimate the spe-

Question

-ed b4 braking
The answer is 80m/s, but how do u get this.

Answer 1

v^2=u^2 + 2as (3rd equation of motion) where v=final velocity (0); u = initial velocity; a=acceleration (-10 m/s^2) and s=distance (320m). So u^2 = 2as = 2 x 320 x 10 = 6400. This gives u = 80 m/s

Answer 2

The change in velocity due to acceleration is dV = at. In your problem velocity starts at V0 (what you want to find) and ends up 0, so the velocity change is V0. Therefore the time it took to stop is V0/a. For a constant acceleration, the stopping distance is s = .5*a*t^2. Substituting for t, you get s = .5*a*(V0^2/a^2) or
s = ,5*(V0^2)/a. Solving for V0 you get

V0 = sqrt(2a*s) = sqrt (2*320*10) = sqrt(6400) = 80

Answer 3

You study hard in school and learn the deceleration formulas.