Can Projectile Motion Be Solved with Given Initial Speed and Angle Alone?

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Homework Help Overview

The discussion revolves around a projectile motion problem where a ball is thrown at an initial speed of 25.0 m/s at an angle of 40 degrees above the horizontal. The ball lands at the same height from which it was launched, prompting questions about whether the distance traveled or the time of flight can be determined with the given information.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to solve for time and distance but is hindered by the condition that the initial and final velocities are the same. They question if additional information is needed to solve the problem.
  • Some participants suggest using standard projectile motion equations to analyze the x and y components of motion, prompting a discussion about initial and final conditions.
  • Others express confusion about rearranging equations due to the symmetry of the motion, particularly regarding the velocities at launch and landing.
  • One participant encourages thinking in terms of positions rather than velocities, hinting at a condition that must be satisfied when the object reaches the ground.

Discussion Status

The discussion is ongoing, with participants exploring different approaches to the problem. Some guidance has been offered regarding the use of projectile motion equations, but there is no explicit consensus on the next steps or resolution of the problem.

Contextual Notes

Participants are grappling with the implications of the ball landing at the same height as its launch point, which affects the analysis of time and distance. The original poster's mention of kinematic equations indicates a focus on the constraints of the problem.

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Homework Statement



Vi=25.0 [tex]m/s[/tex]
[tex]\Theta[/tex]=40.0 above the x-axis

You throw a ball at 40 degrees above the horizon at an initial velocity of 25 m/s

The ball lands at the same height as which it was launched.

Is it possible to find the distance traveled (either vertical or horizontal) or the time it took for the ball to land.

Homework Equations



Kinematic equations.

The Attempt at a Solution



Seems like this would be pretty simple. but trying to solve for time of distance always is hampered by the initial and final velocities being the same.

So would there be more information needed to solve this?
 
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You need to use the standard projectile motion equations describing the x and y components of position as a function of time.

[tex]x(t)=v_0\cos(\theta)t+x_0[/tex]

[tex]y(t)=y_0+v_0\sin(\theta)t-\frac{gt^2}{2}[/tex]

What are your initial conditions? What are your final conditions? How can you use these equations to find the final time, and then the distance traveled?
 
jhae2.718 said:
You need to use the standard projectile motion equations describing the x and y components of position as a function of time.

[tex]x(t)=v_0\cos(\theta)t+x_0[/tex]

[tex]y(t)=y_0+v_0\sin(\theta)t-\frac{gt^2}{2}[/tex]

What are your initial conditions? What are your final conditions? How can you use these equations to find the final time, and then the distance traveled?

Yeah but since it lands as the same horizontal as its launch the velocities are the same.

Trying to rearrange the equations creates a situation where

Since Vi = (25 cos (40)i, 25 sin (40)j) m/s
Vf = ((25 cos (40)i, -25 sin (40)j) m/s

Anyway i rearrange the KEs to solve to t or r doesn't make sense.
 
Think in terms of positions, not velocities. What condition must be true if the object reaches the ground?
 
Last edited:

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