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How to solve for Initial velocity Problem

  • #1

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?
 

Answers and Replies

  • #2
NascentOxygen
Staff Emeritus
Science Advisor
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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.
 
  • #3
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
 
  • #4
NascentOxygen
Staff Emeritus
Science Advisor
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1,071
The problem states clearly what the sled's final speed is. The unknown here is its initial speed.
 
  • #5
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
 
  • #6
NascentOxygen
Staff Emeritus
Science Advisor
9,244
1,071
The sled is brought to a stop, which tells you its final speed is 0 m/s.
 
  • #7
o damn, right under my nose.
 

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