If the girl is accelerating at
First we’ll show the math, a derivation of the solution (in 6 steps). Then, we’ll explain each step in more detail.
1) Why did we choose this formula? Well, the second sentence asks a question containing the key phrase "increase ....speed". Ask yourself, what equations involve changing speed (due to a force or acceleration). There are two
The 1st equation describes the change in speed when an object (or girl in this case) experiences an acceleration,
The 2nd equation describes the change in speed when an object experiences an acceleration,
We chose the first equation here because the phrase "how long" refers to length of time!
What do the physical quantities (variables) in the equation we've chosen represent?
2) In the 2nd step, we're just subtracting
3) Here, we're just dividing both sides by
4) Uh oh! we don't know the initial and velocities
5) They tell us in the problem that the girl's acceleration
6) The last step is arithmetic. We just divide to find