An Alternate Solution for Example 2

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Example 2:

A boat, initially moving at 20 m/s is only moving at 2.0 m/s in the same direction, 25 seconds later. Assuming that the boat's acceleration was constant, what was the boat's acceleration during this time?

Solution:

vo = 20 m/s

v = 2.0 m/s

= 25 s

a = ?

Here's the plan: you can find the acceleration from the equation , but we don't know . However, you can find from the equation , then substitute...

, but:

= 2.0 m/s - 20 m/s = -18 m/s

The boat's acceleration is 0.72 m/s², in the direction opposite to the boat's velocity.

Note:

This is a 2-step solution since you have to find as an intermediate step, but each step is pretty simple.

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