What Is the Change in Velocity and Acceleration of a Rebounding Ball?

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Homework Help Overview

The discussion revolves around a physics problem involving the change in velocity and acceleration of a ball that rebounds after hitting a wall. The scenario describes the ball's initial and final velocities, with a focus on understanding the vector nature of velocity and the calculation of acceleration during the impact.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants explore the calculation of change in velocity by considering the direction of motion and the signs associated with the velocities. There is discussion about whether the change in velocity should be calculated as a simple difference or if it requires consideration of vector direction.

Discussion Status

Participants are actively questioning the assumptions regarding the direction of velocity and how to properly calculate the change in velocity. Some have suggested using negative values for westward motion, while others are clarifying the relationship between speed and velocity. The discussion is ongoing with no clear consensus yet.

Contextual Notes

There is a focus on the definitions of velocity and speed, as well as the implications of direction in the calculations. The time duration of the impact is also mentioned as a factor for calculating acceleration, but specific values and methods remain under discussion.

Speeder63
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Homework Statement


A ball moving westward at 36 m/s hits a wall and rebounds at 27 m/s, eastward. (a) What is the change Δv in the vector velocity? (This is effectively the velocity of the rebounding ball relative to an image of it passing through the wall unaffected. It’s not the same as the 9 m/s reduction in the scalar speed!)

(b) Find the acceleration during the impact if that lasts 0.14 s.

2. The attempt at a solution

For change in velocity I had 9 m/s eastward. I don't know if that is correct.
 
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If we take positive direction as being Eastward then the ball's velocity prior to impact is -36 m/s (that's a minus sign there).

What is the velocity after impact?

What is the second one minus the first one?
 
so the velocity after impact is -9m/s.
would I use this to find the acceleration?
 
andrewkirk said:
If we take positive direction as being Eastward then the ball's velocity prior to impact is -36 m/s (that's a minus sign there).

What is the velocity after impact?

What is the second one minus the first one?
would I use that to find the acceleration?
 
Speeder63 said:
so the velocity after impact is -9m/s.
No.
The absolute value of the velocity has to equal the speed.
 
andrewkirk said:
No.
The absolute value of the velocity has to equal the speed.
So if the velocity is -9m/s the absolute velocity is 9m/s?
 

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