SOLUTION: Can someone please help me with this question? An airplane lands on a runway that is 250 m long. Assume that it uses all of that length to stop and that its velocity upon touchdow

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Question 169699: Can someone please help me with this question?
An airplane lands on a runway that is 250 m long. Assume that it uses all of that length to stop and that its velocity upon touchdown is 65 m/s. What is the acceleration of the plane?
My choices are:
a. 0.13 m/s^2
b -0.13 m/s^2
c. 8.45 m/s^2
d.-8.45 m/s^2
Thanks so much for your help =) !!!!!!
Answer by scott8148(6628) About Me  (Show Source):
You can put this solution on YOUR website!
the initial velocity is 65m/s and the final velocity is zero, so the average velocity is 32.5m/s

the time to stop is 250m / 32.5m/s or 7.69s

the acceleration is 65m/s / 7.69s or 8.45m/s^2

since the acceleration is opposite to the direction of motion (deceleration), it is NEGATIVE