## 6 thoughts on “5.9”

1. Andrew Torres says:

Paul,

After working and viewing your solutions for Problems 9 and 10, I am confused about the substitution made for theta in the step before the small angle assumption is used (2 steps before the boxed answer).

In problem 9, (theta - pi) was plugged in, but in problem 10, (phi + pi/2) was used. Why is this?

1. tutorpaul says:

Oh, that is an error. In this problem I should have plugged in $\theta = \phi + \pi$, I accidentally plugged $\phi$ in as $\theta$. The line you are referencing should read:

The lines after that are correct.

2. Tyler Paschal says:

Shouldn't the acceleration in the r-direction be a negative 4*l/3???

1. tutorpaul says:

Yes, if you look at the image of the worked out problem below the video you will see the correction has already been made!

I found some of these sorts of errors in the middle of editing the videos immediately before posting them. I intent to go back and re-record the problems where errors exist, but it is hard (and unpaid) work so I haven't done it yet.

3. valeserranou says:

shouldn't theta double dot be 4/27 instead of 16/27?