Posted by **eric** on Monday, August 8, 2011 at 2:36am.

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?

- science 10 -
**drwls**, Monday, August 8, 2011 at 5:53am
(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

- science 10 -
**YASH**, Monday, August 8, 2011 at 1:15pm
u=22.2m/s

a=-2.8m/s2

v=8.2m/s

t=?

v=u+at (equation)

8.2=22.2+(-2.8)t

8.2-22.2=-2.8t

-14=-2.8t ('-' sign is cancelled from both the sides)

14/2.8=t

5=t

hence time taken is 5 seconds

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