How to solve for Initial velocity Problem

[pennywise1234]

Homework Statement

A bobsled glides down a hill with an acceleration of -4.5 m/s If it stops after 5 s, what was its initial velocity?

2. Homework Equations
i know vf(final)= v + at

The Attempt at a Solution

i multiplied -4.5m/s by 5s and i got the correct answer the only problem is the answer is negative, i need it to be positive. Where or what did i do wrong?

 

[NascentOxygen]

Homework Statement

A bobsled glides down a hill with an acceleration of -4.5 m/s If it stops after 5 s, what was its initial velocity?

2. Homework Equations
i know vf(final)= v + at

The Attempt at a Solution

i multiplied -4.5m/s by 5s and i got the correct answer the only problem is the answer is negative, i need it to be positive. Where or what did i do wrong?

Write the equation you are using to solve this problem, then substitute in it for the variables you know.

 

[pennywise1234]

The issue is I do not know what equation to use. I though the initial velocity equation would help, but I am not given final velocity I only have two known variables

 

[NascentOxygen]

The problem states clearly what the sled's final speed is. The unknown here is its initial speed.

 

[pennywise1234]

so distance over time ?

i know the equation for for final velocity is vf= v(initial) + (a)(t)<---- acceleration multiplied by time

to get the final velocity i did do distance over time giving me -0.9 then i multiplied -4.5m/s by 5s i added all those figures together giving me a number that is not similar to the answer key

 

[NascentOxygen]

The sled is brought to a stop, which tells you its final speed is 0 m/s.

 

[pennywise1234]

o damn, right under my nose.