Is the Velocity negative or positive?

  • #1
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Member warned about re-posting the same problem statement in new threads. Infraction points awarded.

Homework Statement


If you were to throw a large log over the edge of the Grand Canyon and it took 5.65 seconds to hit the ground, calculate the velocity of the log at impact in m/s and calculate the distance the log fell in feet.[/B]


Homework Equations


vf=vi+at[/B]


The Attempt at a Solution


So I get vf=(9.8)(5.65)= 55.4 ...But then I think about it, and the object is going downwards so shouldn't it's velocity be negative (South)..? Also, is 9.8 supposed to be positive or negative?[/B]
 

Answers and Replies

  • #2
NascentOxygen
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You can choose g to be positive or negative, whichever you wish. The final velocity here will take on whatever sign you give to g. The important thing is that you remain consistent! :)
 
  • #3
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You can choose g to be positive or negative, whichever you wish. The final velocity here will take on whatever sign you give to g.
So there's always two right answers?
 
  • #4
NascentOxygen
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So there's always two right answers?
Not really. It's final velocity is 55.4 m/s towards the centre of the Earth. That's one answer. :)

I'd be concerned about your omission of the units when talking of velocity, though.
 
  • #5
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Not really. It's final velocity is 55.4 m/s towards the centre of the Earth. That's one answer. :)

I'd be concerned about your omission of the units when talking of velocity, though.
Sorry, haha *m/s. One last question, is acceleration the same for all objects?
Well, it is, due to gravity (9.8m/s^2) ..but then again I get confused because there's so many different word problems with different accelerations as answers, obviously. What would be the final, true answer though?
 
  • #6
NascentOxygen
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Sorry, haha *m/s. One last question, is acceleration the same for all objects?
g is the same for all objects in a particular location. Whether the object is accelerating depends on the net force. Gravity is only one of many forces that may be acting simultaneously on an object.

Well, it is, due to gravity (9.8m/s^2) ..but then again I get confused because there's so many different word problems with different accelerations as answers, obviously. What would be the final, true answer though?
The answer to what?
 

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