# Is the Velocity negative or positive?

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1. Feb 5, 2015

### rasofia77

• Member warned about re-posting the same problem statement in new threads. Infraction points awarded.
1. The problem statement, all variables and given/known data
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.

2. Relevant equations
vf=vi+at

3. 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?

2. Feb 5, 2015

### Staff: Mentor

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. Feb 5, 2015

### rasofia77

So there's always two right answers?

4. Feb 5, 2015

### Staff: Mentor

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. Feb 5, 2015

### rasofia77

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. Feb 5, 2015

### Staff: Mentor

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.