What's the hight of a million pennies

1 answer:

3 0

The thickness of a brand new US penny that hasn't been
worn down is 1.52 millimeters.

If you have a million pennies, there are many ways to arrange them.
You can pile them all in one pile, or shovel them into many piles, or
stack them up in any number of stacks up to a half-million stacks
with two pennies in each stack, or try somehow to stack them all up
in one stack that's a million thicknesses high.

Any stack with 'n' pennies in the stack is 1.52n millimeters high.

If you somehow succeed in stacking all million of them in one stack,
then the height of that stack would be . . .

   (1,000,000) x (1.52 mm) = 1,520,000 millimeters
   152,000 centimeters
   1,520 meters
   1.52 kilometers

(about 59,842.5 inches
4,986.9 feet
   1,662.3 yards
   7.56 furlongs
0.944 mile
      all rounded)

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Not much can be done without knowing what $\mathbf F(x,y,z)$ is, but at the least we can set up the integral.

First parameterize the pieces of the contour:

$C_1:\mathbf r_1(t_1)=(2\sin t_1,2\cos t_1,0)$
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where $0\le t_1\le\dfrac\pi2$ and $0\le t_2\le1$ . You have

$\mathrm d\mathbf r_1=(2\cos t_1,-2\sin t_1,0)\,\mathrm dt_1$
$\mathrm d\mathbf r_2=(1,3,3)\,\mathrm dt_2$

and so the work is given by the integral

$\displaystyle\int_C\mathbf F(x,y,z)\cdot\mathrm d\mathbf r$
$=\displaystyle\int_0^{\pi/2}\mathbf F(2\sin t_1,2\cos t_1,0)\cdot(2\cos t_1,-2\sin t_1,0)\,\mathrm dt_1$
${}\displaystyle\,\,\,\,\,\,\,\,+\int_0^1\mathbf F(2+t_2,3t_2,3t_2)\cdot(1,3,3)\,\mathrm dt_2$