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Question
A swimmer bounces straight up from a diving board and falls feet first into a pool. She starts with a velocity of 4.00 m/ s, and her takeoff point is 1.80 m above the pool. (a) How long are her feet in the air? (b) What is her highest point above the board? (c) What is her velocity when her feet hit the water?
1. $1.14 \textrm{ s}$
2. $0.82 \textrm{ m}$
3. $-7.16 \textrm{ m/s}$
Solution Video

# OpenStax College Physics Solution, Chapter 2, Problem 46 (Problems & Exercises) (7:13)

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Submitted by amichon on Thu, 09/17/2020 - 15:45

Why did you use the acceleration due to gravity as a positive 9.80 instead of -9.80?

Submitted by ShaunDychko on Fri, 09/18/2020 - 11:37

Thanks for the question amichon, the formula 2.76 already accounts for the direction of gravity's acceleration. There's a negative in the formula already. $g$ is always meant to be the magnitude of the acceleration due to gravity, so it always gets substituted with positive 9.80. It's a matter of personal preference though. You might see some professors use a plus in their formula, and then substitute -9.80, giving the same result in the end.
Best,
Shaun