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## Homework Statement

An object is thrown vertically upward at 35 m/s. The velocity of the object 5.0 seconds later is:

## Homework Equations

v

_{f}=v

_{o}-gt

## The Attempt at a Solution

g=9.8 m/s

v

_{o}=35 m/s

t=5s

v

_{f}=?

v

_{f}=35-(9.8)(5)=14 m/s down

I know this is the correct answer, but I'm confused about why you choose the equation above. The first time I worked this problem I tried to use v

_{f}=v

_{o}+gt. Could someone please explain to me why this would be wrong? Is it maybe because the acceleration is negative?