Finding Velocity given angle and distance.

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Homework Help Overview

The problem involves determining the initial velocity of an object thrown at a 45-degree angle that travels a horizontal distance of 60 meters before hitting the ground. The discussion centers around the application of projectile motion principles.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants explore the relationship between horizontal and vertical components of velocity, questioning the calculations of time in the air and the use of trigonometric values for angles. There is an attempt to derive the initial velocity using the equation for projectile motion.

Discussion Status

Some participants have provided guidance on re-evaluating the approach to the problem, suggesting that the vertical and horizontal speeds are equal at a 45-degree launch angle. There is ongoing exploration of the correct relationships and calculations needed to find the initial velocity.

Contextual Notes

Participants are discussing the implications of using trigonometric functions and the assumptions related to the angle of projection. The conversation reflects a mix of attempts to clarify the problem setup and the mathematical relationships involved.

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Homework Statement


The questions is, that if you throw something at exactly 45 degrees above the horizontal and it travels 60 m before hitting the ground what's it velocity?


Homework Equations


Physic's equation, see below


The Attempt at a Solution



Horizontal Component
Vh = cos 45
= 0.707

now t = 60/0.707
=84.86

Vertical Component
Vv = 0.707 - gt

What do I do now? Am I right to this point as well?
 
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Welcome to PF.

The first thing to do is start over.

Thrown at 45 degrees means that vertical and horizontal speeds are the same.

So how long is it in the air? Vy/g is the time to go up ... so total time (up and down) is 2*Vy/g

And how fast is it going to go 60 m?

a = 60 = Vx*t = Vx*2*Vy/g

Since Vx = Vy then just solve.
 
LowlyPion said:
Welcome to PF.

The first thing to do is start over.

Thrown at 45 degrees means that vertical and horizontal speeds are the same.

So how long is it in the air? Vy/g is the time to go up ... so total time (up and down) is 2*Vy/g

And how fast is it going to go 60 m?

a = 60 = Vx*t = Vx*2*Vy/g

Since Vx = Vy then just solve.


Ok cool, so is Vy cos 45 = 0.707? so then Vy = Vx = 0.707?
 
odyssey4001 said:
Ok cool, so is Vy cos 45 = 0.707? so then Vy = Vx = 0.707?

No.

.707 is merely the value of cos45 and sin45.

Your mission is to figure out what the initial velocity is.
 
LowlyPion said:
No.

.707 is merely the value of cos45 and sin45.

Your mission is to figure out what the initial velocity is.

ok so is this right,

Vo = [tex]\sqrt{(g*d)/(2 sin Theta*cos Theta)}[/tex]

Vo = [tex]\sqrt{(9.8*60) / (2 sin 45*cos 45)}[/tex]

Vo = 24.24
 
That would be correct.
 

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