I kinematics can someone carefully check my work

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Homework Help Overview

The discussion revolves around the kinematics of three identical balls thrown from the same height with the same initial speed, each at different angles: horizontally, upward, and downward. Participants are examining the motions of the balls and comparing their speeds upon reaching the ground, while disregarding air resistance.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to describe the trajectories of the balls and their final velocities, suggesting that ball c is the fastest, followed by ball b, and then ball a. Some participants question this reasoning, particularly regarding the final velocities of balls b and c, and whether they will hit the ground with the same speed.

Discussion Status

The discussion is ongoing, with participants exploring different interpretations of the problem. Some guidance has been offered regarding the conditions under which balls b and c may have the same final speed, but no consensus has been reached yet.

Contextual Notes

Participants are considering the implications of the initial angles and the vertical components of the velocities, as well as the effects of gravity on the motion of the balls. There is an emphasis on the assumptions made about the angles and initial conditions of the throws.

squintyeyes
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three identical balls are thrown from the same height with the same initial speed...ball a is thrown horizontally, ball b is thrown upward at some angel above the horizontal and ball c is thrown at some angle below the horizontal...disregard air resistance and describe the motions of the three balls and compare the speeds of the balls when they reach the ground.


I think the aswer would go like this however i have reason to believe there is something wrong with this.

The motion of ball a will resemble an upside down parabola where zero starts at the maximum

pic 1

ball b will resemble a parabola as well but it will go up first then down. the reason being that the inital velocity will be counteracted by the acceleration of gravity downwards until the velocity is zero. when the velocity is zero that is the maximum and then the ball b will fall down to earth

pic 2

ball c will resemble the downward part of a parabola since it is only going down.

pic 3

in terms of final velocity it will be ball c being fastest, then ball b, then finally ball a being slowest.

the reason for ball c being the fastest is because you are throwing it down at an initial speed while it is being accelerated down at the acceleration of gravity.

the reason that ball b is faster than c is because at ball b's peak and ball c's peak they only have force of gravity in the y direction to speed the ball up. However, ball b is at a higher height so it will have a larger velocity when it hits the ground.
 

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v^{2}=v^{2}_{0}+2ay

What does that equation tell you about the velocity of b and c? Hint: c will not necessary hit the ground at a higher speed than b.
 
Last edited:
I am lost does that mean that ball b and c will hit the ground with the same velocity and why?
 
Last edited:
If they are launched at plus or minus the same angle with respect to horizontal. i.e. if the magnitude of the vertical component of their velocity is equal, they will land with the same speed.
 
thanks
 

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