How to calculate projectile off cliff when angle is below th

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Homework Help Overview

The problem involves a stone being thrown downwards from a 50 m tall cliff at an angle of 22 degrees below the horizontal with an initial velocity of 12 m/s. The objective is to determine the time it takes for the stone to hit the ground.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to calculate the time to hit the ground using kinematic equations but expresses confusion about the results. Some participants question the treatment of the initial vertical velocity component and whether it should be considered in the calculations.

Discussion Status

Participants are actively discussing the components of the initial velocity and the implications of the angle of projection. There is a recognition of the need to clarify the initial vertical velocity and its role in the calculations.

Contextual Notes

There is a mention of the correct answer being 2.77 seconds, which the original poster is struggling to reach. The discussion includes considerations of how the angle affects the initial velocity components.

Abcdefghijk

Homework Statement


Cliff is 50 m tall
Stone thrown downwards with velocity of 12 m/s and 22 degrees below horizontal
What is the time it will take to hit the ground?


Homework Equations


V=d/t
D= Vi t + 1/2at^2

The Attempt at a Solution


Vx1= cos (22)(12)
= +11.12620625
Vy1= sin (22) (12)
= -4.495279121

I solved the triangle (hyp=12) but from here I am not sure what to do. Here is what I attempted from here:

Vertical
(Vi= 0 m/s, a (g)= -9.81 m/s^2, d= 50 m)
d= Vi t + 1/2at^2
t (re-arranged) = square root of d/(1/2a)
t= 10. 1936792 s

Horizontal
(V= 12 m/s, t= 10.1936792 s)
v= d/t
d= vt
d= (12)(10...)
d= 122.324159 m

The correct answer is 2.77 seconds, but I am unable to get this answer and comprehend how to achieve this answer. I would greatly appreciate a walkthrough/explanation of this question and if the angle was above the horizontal as well.

Thanks

 
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Abcdefghijk said:
d= Vi t + 1/2at^2
t (re-arranged) = square root of d/(1/2a)
t= 10. 1936792 s
What happened to vi t? Isn't there a downward initial velocity component?
 
For the vertical component, the initial velocity should be 0 m/s since the movement is horizontal. Therefore I think that you can eliminate Vi t as it will yield 0.
 
Abcdefghijk said:
Stone thrown downwards with velocity of 12 m/s and 22 degrees below horizontal
This means what is says. The stone is not shot horizontally. In fact you calculated its vertical component here
Abcdefghijk said:
Vy1= sin (22) (12)
= -4.495279121
What do you think Vy1 is?
 
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