6. decelerating a plane at a uniform rate of -8 m/s2, a pilot stops the plane in 484 m. how
fast was the plane going before braking begins?

88 m/s

Explanation:

If we are talking about an acceleration at a uniform rate, we are dealing with constant acceleration, hence we can use the following equation:

(1)

Where:

Is the final velocity of the plane (we know it is zero because we are told the pilot stops the plane at a specific distance)

Is the initial velocity of the plane

is the constant acceleration of the plane

is the distance at which the plane stops

Isolating   from (1):

(2)

(3)

Finally:

This is the veocity the plane had before braking began

object 2 because all the other ones are wrong