Center of mass of baseball bat problem

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Homework Help Overview

The problem involves finding the x coordinate of the center of mass of a baseball bat with a non-uniform linear density defined by the equation \(\lambda = \lambda_0 (1 + \frac{X^2}{L^2})\). Participants are exploring the implications of this density function on the calculations required to determine the center of mass.

Discussion Character

  • Exploratory, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants discuss the need for integration to find both the center of mass and the total mass. There are questions about the correct setup for these integrals and the role of the linear density in the calculations.

Discussion Status

The discussion is ongoing, with participants providing insights into the integration process and questioning each other's calculations. Some guidance has been offered regarding the integration limits and the form of the integrands, but no consensus has been reached on the final results or methods.

Contextual Notes

There are indications of confusion regarding the integration steps and the cancellation of terms, particularly concerning the presence of \(\lambda_0\) in the final expressions. Participants are also clarifying the boundaries of integration and the implications of the density function on the mass calculations.

nns91
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Homework Statement



A baseball bat of length L has a peculiar linear density given by \lambda = \lambda0 * (1+X2/L2)

Find the x coordinate of the center of mass in terms of L

Homework Equations



Mxcm= mr

The Attempt at a Solution



So I use integration

The integrand I have is x*\lambda dx and substitue whatever on the right side of the \lambda equation in. Then I just took normal integral.

However I got wrong answer. The right answer does not contain \lambda0 but mine does

Can you guys help me ??
 
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You need to also do an integration to find the total mass, M. This will have a factor lambda_o that will cancel the one you have on the right side.
 
How do I integrate to find mass M ??

Do I plug in lamda formula*L for M or do I have to integrate lamda*L ??
 
M = int(lambda * dx) will do the job where you take the integral over the length 0 to L.
 
I got (L^2/2 +L^3/4)/(1+L^2/3)

But it's still not the answer in the book.

Did I do something wrong ??
 
You've almost got it looks like to me.
But the numerator should have been multiplied by x

yielding as an integrand x + x3/L2

that gives

x2/2 + x4/4 | from 0 to L or ... 3L2/4

The total Mass looks integrated a little off.

Shouldn't that be (L + L/3) = 4L/3 ?

Then dividing denominator into numerator

(3/4L2)/(4/3*L) = 9L/16
 
Last edited:
How can you get 3L^2/4 and 4L/3

I thought the integral of the total mass will yield L+ L^3/3 ?
 
nns91 said:
How can you get 3L^2/4 and 4L/3

I thought the integral of the total mass will yield L+ L^3/3 ?

The integrand for the volume of the mass is 1 +X2/L2 |evaluated between 0 and L

That yields the result X + X3/3L2 The 0 terms are of no account leaving L + L3/3L2 = L + L/3 = 4L/3

The integrand for the incremental moments is as I outlined previously.
 

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