#### In order to solve the problem:

An airplane accelerates down a runway in order to take off
but aborts and applies brakes causing the plane to stop. The plane
speeds up at a constant rate for 5 seconds, then slows down at the same
rate when the brakes are applied. The plane stops at a point that is
100 meters from its initial position. What was the acceleration of the
airplane during the first 5 seconds?

#### Someone suggests the following procedure:

(A) The acceleration of the plane is constant and the same for the
entire motion.

(B) The entire process takes 10 seconds and the displacement is 100
meters.

(C) It is possible, therefore, to use the formula “change in x =
v_{o,x} t + 1/2 a_{x} t^{2}”, where
v_{o,x} is zero and t = 10s.

(D) The only unknown in this equation is a_{x}, so solve for it.

Which of the following is true?

- The procedure is invalid because statement A is incorrect.
- The procedure is invalid because statement B is incorrect.
- The procedure is invalid because statement C is incorrect.
- The procedure is invalid because statement D is incorrect.
- The procedure is invalid because more than one statement is incorrect.
- The procedure is valid.