- #1

Fascheue

This is simple for more straight forward problems. If they give you mass and acceleration and ask you to find the force, you have all parts of the equation f = ma except for one.

Sometimes I find it confusing though when this is not the case, for example I had to solve a problem something like this:

There are two boats. One boat is 20 units west of the other. That boat starts moving west with a velocity of 19 units/hr. The other boat starts moving north at a velocity of 25 units/hr. What is the rate of change of the distance between the boats in 7 hours.

I eventually solved the problem, but I did so just by trying a ton of different things, many of which did not work. Eventually I set up a right triangle, with one side 20 + 19t, another side 25t, and an unknown hypotenuse. I plugged in 7 for t to get c. Then I implicitly differentiated A^2+B^2=C^2 and plugged in for all value except for the unknown dc/dt to find the answer.

What should be the thought process when solving this problem? I know how to solve it, but how do you know how to solve it? You can’t just find an equation where you have all of the known values except for 1.