- #1
tawnyman
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just a quick question! will the final velocity of a free falling object always be negative even if the answer is positive?
Calculating Final Velocity of Free Falling Objects
- Thread starter tawnyman
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In summary, the final velocity of a free falling object can be positive or negative depending on how you define the sign convention. In the given example, if down is defined as negative, then the final velocity of the cliff diver would be -44.6m/s. However, if up is defined as negative, then the final velocity would be 44.6m/s. The sign convention is arbitrary and the answer may change based on how it is defined.
- #2
cepheid
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tawnyman said:
Hi, welcome to PF!
Sign conventions are arbitrary. It's up to you whether you define "up" to be the positive direction, or "down" to be the positive direction.
That having been said, if you have defined "down" to be negative, and you know that an object is supposed to be moving downward, yet you get a positive answer for its velocity, then your answer is incorrect given the sign convention you chose.
- #3
Doc Al
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tawnyman said:
Not sure what you mean by 'final' velocity, but something in freefall can be moving up or down depending upon the exact problem. (Or not moving at all, for an instant.)
- #4
tawnyman
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thanks so much! that's what i thought, but then there's this question i was trying out (don't worry, it's not homework. found it online so i could practice):
A cliff diver from the top of a 100 [m] cliff. He begins his dive by jumping up
with a velocity of 5 [m/s]. What is his velocity right before he hits the water?
if down is defined as negative and the equation used is vf^2=vi^2+2ad then the answer should be 44.6m/s but the answer on the site was -44.6m/s.
A cliff diver from the top of a 100 [m] cliff. He begins his dive by jumping up
with a velocity of 5 [m/s]. What is his velocity right before he hits the water?
if down is defined as negative and the equation used is vf^2=vi^2+2ad then the answer should be 44.6m/s but the answer on the site was -44.6m/s.
- #5
Doc Al
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He's moving down so his velocity should be negative. The site's answer is correct.tawnyman said:
- #6
tawnyman
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i MUST be doing something wrong.@_@ or I'm inputting something wrong in my calculator. so the square root of 5^2 + 2(-9.8)(-100) is positive?
- #7
Doc Al
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The calculator only gives you the positive square root of a number. You have to supply the negative sign based on your understanding of how he's moving. (Don't forget that a negative number squared is positive.)tawnyman said:
- #8
tawnyman
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Doc Al said:
that's totally the answer to my first question.=D thanks!
FAQ: Calculating Final Velocity of Free Falling Objects
How do you calculate the final velocity of a free falling object?
The final velocity of a free falling object can be calculated using the formula: Vf = Vi + at, where Vf is the final velocity, Vi is the initial velocity (usually 0 in free fall), a is the acceleration due to gravity (9.8 m/s^2), and t is the time in seconds.
What is the acceleration due to gravity?
The acceleration due to gravity is a constant value of 9.8 m/s^2, which means that for every second an object falls, its velocity will increase by 9.8 meters per second.
Does the mass of the object affect the final velocity?
No, in a vacuum, the mass of an object does not affect its final velocity in free fall. All objects will fall with the same acceleration due to gravity regardless of their mass.
How does air resistance affect the final velocity of a falling object?
Air resistance, or drag, can slow down the acceleration of a falling object. As the object falls, it will eventually reach a terminal velocity where the force of air resistance equals the force of gravity, causing the object to no longer accelerate.
Is the final velocity of a free falling object always downward?
Yes, in most cases, the final velocity of a free falling object will always be downward, towards the center of the earth. This is due to the force of gravity pulling the object towards the ground.