Motion System Design

In Response

Remote chance of success

I just got around to reading your article in the April issue regarding your wonderful experience at Best Buy. I am absolutely positive you have been pounded with e-mails regarding very similar experiences.

I too have been tested by them recently. I purchased an open box 51-in. HDTV monitor from them. Why not? It gets the same factory warranty and I paid $600 less. I never get their “extra” warranty. The one contingency I had with the salesman was that I get the correct remote with the TV. He promised I would. Well, after trying for several days to get certain functions to work, I called the help line from the manufacturer. I was informed, that in fact, I had the wrong remote. Once I went back to the store, the salesman “looked around” but could not locate any other remote and attempted to assure me I had the right one. When I informed him I did not have the correct remote based on my conversation with the factory, he passed me off to customer service. That was the last he would talk to me. After having to press the manager very strongly I was assured I would get the right remote but due to the store getting ready to relocate he would have to call me with the information of how and when I would get one. After three days of hearing nothing I again had to pursue the management of this store. The next manager told me that open box items were sold as is and I don't get any remote with them and I should read the fine print on the sale tag. So I took the sale tag to the manager to show him that in “FACT” it was NOT written on the tag that one would receive no remote. With evidence in hand I forced them to order me a new and correct remote. Some three weeks later I finally received what I was due.

Needless to say, I have not been back to this store and will probably never return.
Tim Schumann
Campobello, S.C.

Optional projectile solution

Since the “Alternative FWF solution” for problem 275 was published in the May issue, I thought that the following may also be of interest for projectile problems. If the “x” and “y” parametric equations given in the referenced article are solved for time “t” and combined, it is possible to obtain equations for “x” and “y” coordinates that are not functions of time. The following are the required formulas for projectile motion:

First, let x2 - x1 = Dx , y2 - y1 = Dy, Vx = Vcos a, Vy = Vsin a, and L = Vx^2 / g , then :

The original parametric functions of “t” for reference are : Dx= Vx t & Dy = Vy t - g t^2 / 2

The equations resulting from simultaneous solution of the above parametric functions for “t” are :

Dy = Dx tan a - Dx^2 / (2 L) : a parabola.

Dx = L { tan a ± sqrt [ ( tan a )^2 - 2 Dy / L ] }
Lee Ruiz
Peerless Pump
Indianapolis, Ind.

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