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Question
A camera is taking pictures of a falling ball. The acceleration due to gravity used is 980 cm/second^2. The ball has fallen 160 cm in 4/7 of a second and the average velocity is 280 cm/second. I need to find the amount of time between consecutive camera flashes. I have no idea how to do this. Am I supposed to use derivatives? If so, how do I do that?

Answer
While this is clearly a homework problem and I don't do those (per my profile), I can tell you that you that this question makes no sense.  If you just divide the distance (160 cm) by the time (4/7 of a second) then you get 280 cm/s for an average velocity.  So the amount of time between camera flashes is just 4/7 of a second.  There's really no problem here to solve at all, the answer is right there in the problem itself.  It's a non-problem.  It doesn't even ask you what velocity it started at (if you just plug in d=1/2at^2 you get 160 cm which means it was simply falling from rest) or ask for anything that you would need to construct some more complex solution at all.  

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Dr. Stephen O. Nelson

Expertise

I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.

Experience

I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

Education/Credentials
Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.

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