Can I Assume Yi is 0m in Projectile Motion Calculations?

  • Thread starter Thread starter EinsteinApple
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Homework Help Overview

The discussion revolves around a projectile motion problem involving a slingshot launching water balloons at a specific angle and speed. Participants are examining the assumptions regarding the initial and final heights in the calculations.

Discussion Character

  • Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants explore whether it is valid to assume the initial height (yi) is zero when calculating the projectile's motion. There are discussions about the implications of this assumption on the final height (yf) and the consistency of height measurements.

Discussion Status

Some participants have provided insights on the assumptions regarding height, suggesting that if the launch and landing heights are not specified, they may be considered the same. Others have raised questions about the implications of assuming different heights and the need for consistency in measurements.

Contextual Notes

The original problem statement does not specify the launch or landing height, leading to varying interpretations among participants regarding the assumptions that can be made.

EinsteinApple
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Homework Statement


A man builds a slingshot that can launch water balloons. If he launches a water balloon at 45.0 degrees to the horizontal at a speed of 35.0 m/s, how far away will the balloon hit?

Homework Equations


xf=xi + vix t
vfy=viy+at
yf=yi + 1/2(viy+Vfy)t
yf=yi + viyt + 1/2at^2
vfy2 = viy2a + 2ay

The Attempt at a Solution

:

ti = 0
xi=0
yi = 0 (CAN I ASSUME THIS?)
viy = 24.75 m/s
vix = 24.75 m/s
ax=0m/s2
ay=0m/s2
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As long as you are consistent with the interpretation of the other given quantities, yes you can.
 
I just assumed that y2 = 0 because it hits the ground. Therefore, I assumed because he was holding the slingshot y1 couldn't equal 0.
Therefore if y1=0, then y2= a negative value because it's lower.
 
Is the balloon launched at some height above ground? What is that height?
When you write
EinsteinApple said:
yf=yi + 1/2(viy+Vfy)t
yi and yf need to be measured from the same point. That's what what I meant by "consistent".
 
The problem statement says nothing about the launch or landing height so you have to assume they are the same.
 

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