A jet aircraft rolls onto the end of a runway before accelerating down the runway for takeoff. At the point where the aircraft leaves the ground, it is traveling at 100 m/s. If the aircraft's initial speed when it rolled onto the runway was 10 m/s, and it accelerates for 20s before it leaves the ground, what is the magnitude of the aircraft's average acceleration during takeoff?

a = 100 - 10/20 = 4.5 m/s^2
did I do this right?

looks good, except it should be

(100-10)/20

To determine if you calculated the magnitude of the aircraft's average acceleration during takeoff correctly, let's break down the steps:

First, let's calculate the change in velocity of the aircraft during takeoff:
Change in velocity = final velocity - initial velocity

Final velocity = 100 m/s (given)
Initial velocity = 10 m/s (given)

Change in velocity = 100 m/s - 10 m/s = 90 m/s

Next, let's calculate the time it takes for the aircraft to achieve this change in velocity:
Time = 20 s (given)

Now, we can calculate the average acceleration during takeoff:
Average acceleration = change in velocity / time

Average acceleration = 90 m/s / 20 s = 4.5 m/s^2

Therefore, your calculation is correct. The magnitude of the aircraft's average acceleration during takeoff is 4.5 m/s^2. Well done!