An Alternate Solution for Example 5

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Example 5:

An airplane, initially moving at 3.0 m/s down a runway, begins to accelerate down the runway at 3.6 m/s². How far down the runway will it be in 20 seconds?

Solution:

vo = 3.0 m/s

a = 3.6 m/s2

= 20 s

= ?

The plan: We can use to find the distance the plane moves - except that we don't know the plane's average velocity, . We could find the plane's average velocity using the equation , except we don't know the airplane's final velocity, v. Well, we could find the plane's final velocity from the equation . Ha! This is a three-step, round-about solution, but it is a valid solution. It shows that sometimes you just have to get started, and find whatever you can find - then work from there.

Answer: The airplane moves 780 meters in this time.

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