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Question
A ball is thrown straight up with an initial velocity vi= 4.9m/s/ assume the acceleration due to gravity is g=9.8m/s^2 downward.

how long does it take to come back to its initial position?

t=1sec

what is the final velocity of the ball when it returns to the level from which it was thrown straight up.

vf=14.7m/s

Answer
THIS IS OBVIOUSLY A HOMEWORK QUESTION.  

I don't answer homework questions.

One of these two answers is wrong, due to a sign error.

You can find it, this isn't a "find the sign error in my homework" forum.

No, I'm not going to tell you which answer is right or where the obvious sign error is, but after teaching physics in some form or another for about 20 years I can tell you that I know exactly what you did wrong.  Now go find it.

(And, obviously, stop asking me homework questions.)

Physics

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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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