How Do You Calculate Initial Velocities for Projectiles?

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    Resultant Velocity
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Homework Help Overview

The discussion revolves around calculating initial velocities for a projectile launched from a height of 2 meters, landing on the ground after 2 seconds. Participants are exploring the physics of projectile motion, specifically focusing on initial upward and resultant velocities.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants are attempting to apply given equations related to motion but are encountering confusion regarding their applicability. There are questions about the correct interpretation of the problem, particularly concerning the initial upward velocity and the nature of the resultant velocity. Some participants are also questioning the assumptions made about the acceleration due to gravity and the coordinate system to be used.

Discussion Status

The discussion is active, with participants providing guidance on how to approach the problem. There is an emphasis on clarifying the equations and understanding the context of the projectile's motion. Some participants are exploring different interpretations of the questions posed, particularly regarding the second question about resultant velocity.

Contextual Notes

There is mention of constraints such as the assumption of being on the surface of the Earth, which implies a known acceleration due to gravity. Additionally, there is a lack of information regarding the horizontal component of the projectile's motion, which is noted as insufficient for a complete analysis.

Oceanspire
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Poster has been reminded to show their Attempt at a Solution
1. You launch a projectile from a wall that is 2 meters in height. It lands on the ground 2 seconds later.

-What is the initial upward velocity of the projectile at the moment of launch?
-What is the initial resultant velocity of the projectile at the moment of launch?2. Equations given:
- v = at
- d = (1/2)at2
- t2 = d/a

I tried using the last equation to find the acceleration, but I can't seem to figure it out at all.
 
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Your third equation disagrees with your second.
You need to show some attempt, as per the template and guidelines.
 
haruspex said:
Your third equation disagrees with your second.
You need to show some attempt, as per the template and guidelines.
This is my homework assignment and these are the equations that were given to me to use but I don't know how. I just need help. I don't know where to start.
 
Oceanspire said:
I tried using the last equation to find the acceleration
Presumably the setting is the surface of the Earth, so you don't need to find the acceleration, it is already known.
It doesn't say, but I assume you are only asked to find the vertical velocity. There's not enough information to find any horizontal component.
The second question makes no sense. Is that the exact wording?
 
haruspex said:
Presumably the setting is the surface of the Earth, so you don't need to find the acceleration, it is already known.
It doesn't say, but I assume you are only asked to find the vertical velocity. There's not enough information to find any horizontal component.
The second question makes no sense. Is that the exact wording?
Yes, except the first question which I'll fix in a second. I forgot to add that I want to find the initial upward velocity
 
Oceanspire said:
Yes, except the first question which I'll fix in a second. I forgot to add that I want to find the initial upward velocity
Ok.
For the first question:
The first thing to do is choose your coordinate system. Which do you want to make the positive direction, down or up? (Up is sort of standard, but it's your choice.)
You know the acceleration (which is?)
You know the time.
What is the net change in height (d)?
The equation you quote, d = (1/2)at2, is not general enough. It assumes starting from rest, which is not the case here. Can you quote a more standard 'SUVAT' equation?

The second question still makes no sense. My guess is they meant to ask for the velocity just before hitting the ground.
 

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