How to solve for time till object hits ground when thrown upwards off a cliff?

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Homework Help Overview

The discussion revolves around calculating the time it takes for an object thrown upwards from a cliff to hit the ground, given its initial velocity and the height of the cliff. Participants are exploring the dynamics of projectile motion, particularly the effects of gravity on the object's trajectory.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the need to consider both the upward motion and the subsequent downward motion of the object. Questions arise about whether separate calculations are necessary for each phase of the motion and how to account for the height from which the object is thrown.

Discussion Status

The conversation is ongoing, with participants offering insights into the role of gravity and vertical displacement. Some guidance has been provided regarding the use of the quadratic formula for solving the problem, but there is no explicit consensus on the approach to take.

Contextual Notes

There is a focus on the vertical displacement being negative due to the downward direction of the cliff's height, and participants are considering how to integrate the initial height of the throw into their calculations.

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How do you properly solve for the time till an object hits the ground when its thrown upwards off a cliff? With only The initial velocity and the hieght of the cliff. Thx :smile:
 
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What goes up, must come down. It may not have been written but you were also given the acceleration due to gravity. (9.8m/s^2). Gravity is first acting against the object being thrown up, then it will reach a point where v = 0. Then the object will return down as gravity works with the object.
 
But this is going up from the top of the cliff, then down, passing the point where it was thrown. Do you have to do 2 separate calulations?
 
How do you properly solve for the time till an object hits the ground when its thrown upwards off a cliff? With only The initial velocity and the hieght of the cliff.

Find vertical info.
Vertical
d = vt + 1/2(atsquared)
you have v, d is the height of the cliff (a negative value) and you have a(-9.8m/ssquared which is gravity), solve for t using quadratic formula. The time vertically is the same as time horizontally but since you are only looking for time the horizontal info is not necessary.
 
lol but wut about the height that its thrown first, isn't it that plus the hieght of the cliff?
 
No because you are looking for the time when the ball reaches the ground. Therefore you have to ask yourself what will be the vertical displacement for the time you are looking for. It is -d. This makes sense because althought the ball will go up for a certain d, it will also come back down for that same d just in the opposite direction and will continue moving until it has fallen the height of the cliff (-d)
 

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