Vertical Motion Question

  • #1

Homework Statement




A ball is thrown vertically from the edge of a cliff. It rises 10 m above the cliff, then falls 50 m below the cliff.
Find the inital velocity and determine the time the ball was in the air.

Homework Equations



(v final )^2 - (v initial)^2 = 2a (delta y)

The Attempt at a Solution



I'm not sure if I should use 10 or 60 m for the displacement in this equation.

I used 60 m and got v inital = 34. 292 m/s.
 

Answers and Replies

  • #2
Hootenanny
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Homework Statement




A ball is thrown vertically from the edge of a cliff. It rises 10 m above the cliff, then falls 50 m below the cliff.
Find the inital velocity and determine the time the ball was in the air.

Homework Equations



(v final )^2 - (v initial)^2 = 2a (delta y)

The Attempt at a Solution



I'm not sure if I should use 10 or 60 m for the displacement in this equation.

I used 60 m and got v inital = 34. 292 m/s.
Displacement is a vector with a magnitude equal to the distance between the initial point & final point. In this case your initial point is 0m and your final point is -50m.
 
  • #3
tiny-tim
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Homework Helper
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A ball is thrown vertically from the edge of a cliff. It rises 10 m above the cliff, then falls 50 m below the cliff.
Find the inital velocity and determine the time the ball was in the air.

I used 60 m and got v inital = 34. 292 m/s.

Hi veronicak5678! :smile:

I don't get it … what did you use for vfinal? :confused:

(and why 60 rather than 40?)

Hint: you need at least one known v … so what y must you use? :smile:
 
  • #4
I used 0 for v final. And I used 60 because it travels 10 above, then 50 below. So I should just use 50 for delta y?
 
  • #5
tiny-tim
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I used 0 for v final.

Good … but if you use 0 for vfinal, you must use the y where v = 0, which is … ? :smile:
 
  • #6
So I do use 50 for displacement? Using that, I come up with initial velocity = 31.3 m/s, and time in the air = 3.194 s.
 

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