What's the speed of ball when travelling over the fence?

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Homework Help Overview

The problem involves a baseball scenario where a ball is hit with an initial speed and travels over a fence of a specified height. The context includes considerations of energy loss due to air resistance and the relationship between kinetic and potential energy.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the application of energy conservation principles, specifically how to account for the loss of kinetic energy due to air resistance. There are attempts to set up equations relating kinetic and potential energy, with some questioning the correct application of the energy loss factor.

Discussion Status

Participants are actively engaging with the problem, offering hints and prompting each other to reconsider specific aspects of their equations. There is a focus on clarifying which energy term should be halved and ensuring the correct interpretation of the energy conservation principles.

Contextual Notes

There is an emphasis on the initial kinetic energy and how it relates to the energy at the point of crossing the fence. Participants are navigating through potential misunderstandings regarding the setup of their equations and the assumptions made about energy loss.

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Homework Statement


Two girls are playing baseball in a park. The batter hits the 400-g ball with a speed of 20.0 m/s. It travels over the park's fence that is 4.00 m high. Assuming that the ball loses half of its energy to air resistance, at what speed does the ball travel over the fence?

Homework Equations


Ek = 0.5*m*v^2
Ep = m*p*h


The Attempt at a Solution


0.5*(0.4Kg)*(20 m/s)^2 = 0.5 [(0.4Kg)(9.81 m/s^2)((4m) + 0.5(0.4Kg) Vf^2]
My answer was wrong.
 
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Have another think about the first 0.5 on the right of the =.
 
Hoyin said:
0.5*(0.4Kg)*(20 m/s)^2 = 0.5 [(0.4Kg)(9.81 m/s^2)((4m) + 0.5(0.4Kg) Vf^2]
My answer was wrong.

You're line of thinking is correct. Just stress on which energy needs to be reduced by half.
 
I tried reduce the Kinetic energy by half, but the answer is incorrect. Thanks.
 
Hoyin said:
I tried reduce the Kinetic energy by half, but the answer is incorrect. Thanks.
That's not what you've done in your equation. Check again.
 
Hoyin said:
I tried reduce the Kinetic energy by half, but the answer is incorrect. Thanks.
Which term in your equation represents the initial KE? Where is that multiplied by one half?
 

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