Initial Velocity and Acceleration-

[needhelpfast]

Initial Velocity and Acceleration--Please Help!

Homework Statement

You are driving along a straight section of roadway (x-axis). You spot a police officer and apply the brakes, slowing down at a constant rate. Your positions (in meters) at successive time intervals of 0.515 s are tabulated below as function of time. (1) Calculate the initial speed (i.e., the speed at t=0, the time at which the brakes are first applied.). (2) Calculate your acceleration along the x-axis, ax.
NOTE: Both answers must be correct to get credit.
x (m) 6.00 18.46 30.00 40.60
t (s) 0.000 0.515 1.030 1.545

Homework Equations

vi=d/t-at/2

The Attempt at a Solution

First, i found the velocity by doing the slopes, and the points i got were

.2575, 24.194
.7725, 22.408
1.2875, 20.583

i then found the slopes of those to get the acceleration, and i got -3.468 and -3.544. therefore the average acceleration is -3.5 m/s2

i then plugged the acceleration into the equation above and got that the initial velocity would be 25.1 m/s

i'm not sure about this answer, and any help would be greatly appreciated!

 

[needhelpfast]

Please help! This is due really soon!

 

[ehild]

Your solution is OK, but I got 25.4 m/s for the initial velocity, using the first interval.

ehild