Question
A basketball player is running at 5.00 m/s directly toward the basket when he jumps into the air to dunk the ball. He maintains his horizontal velocity. (a) What vertical velocity does he need to rise 0.750 m above the floor? (b) How far from the basket (measured in the horizontal direction) must he start his jump to reach his maximum height at the same time as he reaches the basket?
1. $3.83 \textrm{ m/s}$
2. $1.96 \textrm{ m}$
Solution Video

# OpenStax College Physics Solution, Chapter 3, Problem 46 (Problems & Exercises) (3:30)

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Submitted by katebrackley on Tue, 02/11/2020 - 11:46

hi Shaun, when is g positive 9.8 vs -9.8? Wouldn't it always be negative, since it's acting against the y at all times?

Submitted by ShaunDychko on Tue, 02/11/2020 - 14:43

Hello Kate, $g$ is meant to always be the magnitude of the acceleration due to gravity. Having down be the negative direction is itself a convention, albeit a very common one. Nevertheless, when someone takes down to be the positive direction, the acceleration due to gravity would be $+g$, or $+9.8\textrm{ m/s}^2$. In short, $g$ is always positive, and a negative sign is placed in front when the chosen coordinate system says that down is the negative direction.
Hope that helps,
Shaun