In the first meeting of my mechanics lecture students for the sixth week of classes, I discussed several examples on free fall for all three scenarios and constant acceleration for one dimension in general, using one of the books in the library for which I have a complete solutions manual.

I made all the examples very procedural, first asking whether they believed the description was for horizontal or vertical motion. If it was for vertical motion, they had to determine if it was the first, second or third scenario.

Unlike in the previous meetings though, I did not ask them to work out different parts of the problems on the board. I wrote down everything, solved everything and computed for everything.

This was to ensure that the solution of each problem would be done in record time, and to give them a staggering amount of practice items that they can study at home.

Towards the end there was an inquiry about whether I will be giving any identification type questions. I said, “That depends. Will you consider it too difficult to answer things like: Miles per hour squared is a unit of – blank.” Someone actually answered “Velocity.” So I rested my case.

In one of the examples, I also emphasized to them that for an object going straight up, it will take the same time to reach its maximum height as it takes to go from that height back to original point. This is a shortcut they could use for some of the problems where total time in the air is given and the object returns to the same height. To get the time along one side of the trip, they just have to divide the total.

The last example I gave them had two parts. In the first part, the object has a certain velocity directed downwards. When they had computed for the time elapsed, the second part asked how the time would change if the object’s initial velocity were now directed upwards.

There were at least three ways to solve this that I showed them. First time to maximum height (which had to be determined) and velocity zero was computed, and added to time from the top height to the final point well below the origin.

Second, we could use the computation from the first part, and just solve for the time from an initial velocity and final velocity, which have the same value but different signs.

Third was just applying the initial velocity, the final velocity (to be determined also) and the final displacement (the last two both negative) to an equation where time is computed. This was the easiest.

Session 817 has zero velocity at this point. Class dismissed.