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Over [174]
2 years ago
11

Derive the formula for the moment of inertia of a uniform, flat, rectangular plate of dimensions l and w, about an axis through

its center, perpendicular to the plate. Express your answer in terms of the variables l, w, and M.
Physics
1 answer:
Ad libitum [116K]2 years ago
4 0

Answer:

A uniform thin rod with an axis through the center

Consider a uniform (density and shape) thin rod of mass M and length L as shown in (Figure). We want a thin rod so that we can assume the cross-sectional area of the rod is small and the rod can be thought of as a string of masses along a one-dimensional straight line. In this example, the axis of rotation is perpendicular to the rod and passes through the midpoint for simplicity. Our task is to calculate the moment of inertia about this axis. We orient the axes so that the z-axis is the axis of rotation and the x-axis passes through the length of the rod, as shown in the figure. This is a convenient choice because we can then integrate along the x-axis.

We define dm to be a small element of mass making up the rod. The moment of inertia integral is an integral over the mass distribution. However, we know how to integrate over space, not over mass. We therefore need to find a way to relate mass to spatial variables. We do this using the linear mass density of the object, which is the mass per unit length. Since the mass density of this object is uniform, we can write

λ = m/l (orm) = λl

If we take the differential of each side of this equation, we find

d m = d ( λ l ) = λ ( d l )

since  

λ

is constant. We chose to orient the rod along the x-axis for convenience—this is where that choice becomes very helpful. Note that a piece of the rod dl lies completely along the x-axis and has a length dx; in fact,  

d l = d x

in this situation. We can therefore write  

d m = λ ( d x )

, giving us an integration variable that we know how to deal with. The distance of each piece of mass dm from the axis is given by the variable x, as shown in the figure. Putting this all together, we obtain

I=∫r2dm=∫x2dm=∫x2λdx.

The last step is to be careful about our limits of integration. The rod extends from x=−L/2x=−L/2 to x=L/2x=L/2, since the axis is in the middle of the rod at x=0x=0. This gives us

I=L/2∫−L/2x2λdx=λx33|L/2−L/2=λ(13)[(L2)3−(−L2)3]=λ(13)L38(2)=ML(13)L38(2)=112ML2.

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Explanation:

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Why is the speed of different sounds in a single medium remain the same though wavelength is different?
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2 years ago
A 25 cm diameter circular saw blade spins at 3500 rpm. How fast would you have to push a straight hand saw to have the teeth mov
AURORKA [14]

Answer:

The answer is "45.79 m/s"

Explanation:

Given values:

diameter= 25 cm

w= 3500 rpm

Formula:

\boxed{v=w \times r} \ \ \ \ \ \ _{where}  \ \ \ w  =  \frac{rad}{s}  \ \ \ and  \ \ \ r   = meters

Calculating r:

r= \frac{diameter}{2}

  =\frac{25}{2}\\\\=12.5 \ cm

converting value into meters: 12.5 \times 10^{-2} \ \ meter

calculating w:

w= diameter \times \frac{2\pi}{60}\\

   = 3500 \times \frac{2\times 3.14}{60}\\\\= 3500 \times \frac{2\times 314}{6000}\\\\= 35 \times \frac{314}{30}\\\\= 35 \times \frac{314}{30}\\\\=\frac{10990}{30}\\\\=\frac{1099}{3}\\\\=366.33

w= 366.33 \ \ \frac{rad}{s}

Calculating v:

v= w\times r\\

  = 366.33 \times  12.5 \times 10^{-2}\\\\= 366.33 \times  12.5 \times 10^{-2}\\\\= 4579.125 \times 10^{-2}\\\\\boxed{=45.79 \ \ \frac{m}{s}}

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What is fliud mechanism ​
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The study of forces and flow within fluids.

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3 years ago
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In an inelastic collision, cart A of mass 100kg is moving to the right at 10m/s toward cart B of mass 200kg which is at rest. Th
prohojiy [21]

Answer:

  3.33 m/s to the right

Explanation:

Momentum is conserved, so you have ...

  (m1·v1) +(m2·v2) = (m1+m2)v

  v = (m1·v1 +m2·v2)/(m1+m2)

  = ((100 kg)(10 m/s) +(200 kg)(0 m/s))/(100 kg +200 kg)

  = (1/3)(10 m/s) ≈ 3.33 m/s

The final velocity is about 3.33 m/s to the right.

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