Need to find final Height, Equation not Working

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Homework Statement

Homework Equations

The kinematic equations--namely, S_f = S₀ + V₀Δt

The Attempt at a Solution

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I am a bit confused as it seems this problem is very straight-forward.
My known variables:
X₀ = 0m
Y₀ = 1.7m
Δt = 3.92s
V₀ = 29m/s
Θ = 60^ο
Y_f = ?

So, I just use the above equation for the y-component:

Y_f = Y₀ + V₀y(Δt)

Y_f = 1.7m + 29sin(60) * 3.92s

My final answer is in the hundreds, but the correct answer is 24.85m. Can someone steer me in the right direction, and also tell me why the equation I used doesn't work?

Thanks so much!

 

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Okay, I solved the problem by using Δy = V_0yt + 1/2(a)(t²)

My only question, then, is why doesn't the other equation I used work? And when should I use that other equation?

Thanks.

 

[Zack K]

You should use the form d=(vi)(t)+1/2(g)(t)^2, because you have to take into account that gravity will affect the height reached over the time period.

 

[Zack K]

Okay, I solved the problem by using Δy = V_0yt + 1/2(a)(t²)

My only question, then, is why doesn't the other equation I used work? And when should I use that other equation?

Thanks.

I think it's because your equation assumes that the object travels in a linear path without the affect of gravity.

 

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You should use the form d=(vi)(t)+1/2(g)(t)^2, because you have to take into account that gravity will affect the height reached over the time period.

Understood. So would the other equation only be used for finding horizontal distance since gravity doesn't affect the x-component?​

 

[Zack K]

Understood. So would the other equation only be used for finding horizontal distance since gravity doesn't affect the x-component?​

Exactly :)