Pole Vaulting Kinematics Problem

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Homework Help Overview

The discussion revolves around a kinematics problem related to pole vaulting, specifically analyzing the motion of a pole-vaulter as she leaves the ground with an initial upward speed. The problem includes questions about her speed at a certain height, the time taken to reach that height, and the reasoning behind multiple time solutions for the ascent and descent phases.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants discuss the calculations for speed and time, with one expressing confidence in their answers for the first two parts. The focus shifts to understanding the reasoning behind the two possible answers for the time taken to reach the height, with suggestions that one answer corresponds to the ascent and the other to the descent.

Discussion Status

Participants are actively exploring the implications of the kinematic equations and the nature of the motion involved. There is a productive dialogue regarding the interpretation of the two time solutions, with some guidance offered on how different equations may yield varying results.

Contextual Notes

Participants are navigating the nuances of kinematic equations and the physical context of the problem, particularly the ascent and descent of the pole-vaulter. There is an acknowledgment of potential confusion regarding the interpretation of time measurements in the context of the problem.

physicsnobrain
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Homework Statement


A pole-vaulter leaves the ground with an upward speed of 9.5 m/s.
(a) How fast is she going when she is 2.0 m above the launch point?
(b) How long is required to reach this height?
(c) Why are there two answers to (b)?



The Attempt at a Solution



Question A and B I don't have a problem with. I worked out A to be 7.1 m/s (2 sig digs) and B to be 0.2 seconds (2 sig digs).

However it is question C I am not understanding. I feel tempted to write "because I can write the answer in seconds or I can write it in minutes". But I feel this is a silly answer, therefore I need help.
 
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physicsnobrain said:
However it is question C I am not understanding. I feel tempted to write "because I can write the answer in seconds or I can write it in minutes". But I feel this is a silly answer, therefore I need help.
When the pole vaulter goes up, she must come down.
 
CAF123 said:
When the pole vaulter goes up, she must come down.

So there could be one answer that measures her going up and one answer that measures her going up then coming down?
 
physicsnobrain said:
So there could be one answer that measures her going up and one answer that measures her going up then coming down?
Yes, depending on what kinematic equation you use you will either get the two solutions automatically or not.
 

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