A plane traveling at 80 m/s is slowing down on the runway. In 15 seconds, the plane comes to a complete stop at the gate. How do you calculate the acceleration of the plane?
Acceleration is equal to change in velocity divided by the change in time.
If the plane stops, the finishing speed is 0m/s. As you mentioned, the speed at which the plane is at when it starts to slow down is 80m/s. The change in velocity must therefore be -80m/s (Change in velocity is finishing speed minus starting speed so this number must be a negative)
The time at which the plane started to slow down is 0 seconds, and the plane takes 15 seconds to slow to a stop. The change in time must therefore be 15 seconds.
Hope this helped you!