science 10
posted by eric .
A student driver is travelling at 22.2 m/s and sees a school zone ahead. Using her brakes, she accelerates at 2.8 m/s2 to reduce her velocity to 8.2 m/s. How much time did it take to change her velocity?

(deceleration rate)*(time) = (speed change)
She reduces her speed by 14 m/s, so the change is 14 m/s.
time = (14 m/s)/(2.8 m/s^2)
= 5 seconds 
u=22.2m/s
a=2.8m/s2
v=8.2m/s
t=?
v=u+at (equation)
8.2=22.2+(2.8)t
8.222.2=2.8t
14=2.8t ('' sign is cancelled from both the sides)
14/2.8=t
5=t
hence time taken is 5 seconds