Hi everyone, I feel silly for asking what seems to be such a simple question, bu

Question

Hi everyone,

I feel silly for asking what seems to be such a simple question, but can someone further elaborate on WHY EXACTLY the the velocity is 0 when t = 4sec?

I don't understand why.. even after re-reading Cramster's explanation.

I included the graph, just in case nobody has access to it from the book:

http://img37.imageshack.us/img37/4195/img20100831171117.jpg

Thanks!! :( P.S. Sorry about the picture not being as crisp as I thought it was. But the parabola, and the tangent green line are the only lines you should be looking at :) Anything else is stray markings. http://img37.imageshack.us/img37/4195/img20100831171117.jpg Thanks!! :( P.S. Sorry about the picture not being as crisp as I thought it was. But the parabola, and the tangent green line are the only lines you should be looking at :) Anything else is stray markings.

Explanation / Answer

v = delta x / (delta t) displacement/(elapsed time) The slope of the curve at any time thus represents the speed. The tangent to the curve is the slope of the curve and gives the the instantaneous speed (if the instaneous speed were a constant speed then the curve would just be the straight line shown in the diagram as the tangent) So the slope of the tangent to the curve represents the instaneous speed at that point. The x-axis doesn't show in the image you provided. When the slope is zero (flat) the speed is zero because the instaneous displacement (delta x) is zero while the time is still increasing. In calculus this instaneous speed is called the derivative of the displacement with respect to time.

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