Please help with an acceleration and distance problem

[science_rules]

Homework Statement

A rocket sled goes down a track at a speed of 632 miles/hr. The sled is then brought to a rest in 1.40 seconds. Determine the a) negative acceleration experienced on the sled and b) the distance traveled during the negative acceleration.

Homework Equations

I attempted to calculate the acceleration using the a = change in velocity divided by change in time. The answer in my book was -202 meters/second squared, which i didn't understand because when I tried converting my result to met/sec, it did not match this. it was too much: -661.4 met/sec. i also tried calculating the distance traveled using the distance formula: x= xi + vit + 1/2 at^2 This also didn't work because I realized when I tried converting my answer to met/seconds, it was still way too much. The book's answer was 119 meters. My answer was 1, 495.2 meters. I thought that I used the correct formulas but there must be something I am missing.

The Attempt at a Solution

See above.

 

[mgb_phys]

Be carefull with signs!
The equations are quite simple, v = u + at for the acceleration and v² = u² + 2as for the distance.

 

[science_rules]

ok thanks! i think i was not aware of a few of the simpler equations to use when solving these problems.