Question

A car traveling at 25 m/s starts to decelerate steadily. It comes to a complete stop in 12 seconds. What is its acceleration?

Answer 1

assume it is in uniform deceleration.
u=25
v=0
s=x
a=?
t=12

v=u+at
0=25+a(12)
a=-2.08(3sig fig)

decelerarion of 2.08 ms^(-2)/
acceleration=-2.08ms^(-2)

Answer 2

Acceleration = (change in speed) / (time for the change)

Change in speed = (ending speed) minus (starting speed)

                            =      (0)             -      (25 m/s)     =     -25 m/s

Acceleration  =  (-25 m/s) / (12 sec)  =  -2.083 m/s²  .