The driver of a pickup truck going 100 km/h applies the brakes, giving the truck a uniform deceleration of 6.50 m/s^2 while it travels 20.0 m.
a) what is the speed of the truck in kilometers per hour at the end of this distance?
b) How much time has elapsed?
The Attempt at a Solution
The first thing I did was convert 100 km/h into m/s and got 277.7 m/s.
After converting I tried using V^2= V(initial)^2 x 2(a)x, where a = acceleration and x = horizontal distance.
V^2 = (277.7 m/s)^2 + 2 (-6.50 m/s^2) (20.0-0)
V^2 = 77117.29 + (-260)
V^2 = 76857.29
V= 277.23 m/s which equates to 99.8 km/hr which makes no sense.
I then tried x = x(initial) + 1/2 at^2 to try and acquire time first.
I ended up getting 83 seconds. Which is way off. So I checked the answers in the back of the book and it read:
for part a) 81.4 km/h
b) .794 s
can someone please tell me what I'm doing wrong? I'm obviously not asking for the answer since I've got the book.