Calculating Initial Velocity and Time in Vertical Motion

[veronicak5678]

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.

 

[Hootenanny]

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.

 

[tiny-tim]

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!

I don't get it … what did you use for v_final?

(and why 60 rather than 40?)

Hint: you need at least one known v … so what y must you use?

 

[veronicak5678]

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?

 

[tiny-tim]

I used 0 for v final.

Good … but if you use 0 for v_final, you must use the y where v = 0, which is … ?

 

[veronicak5678]

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.