Disk's Circular Path

Geometry Level 4

A circular disk with an area of 1 1 rolls in a circular path. The disk would move in 36 0 360^{\circ} rolls π \pi times to finish the path. If the path's length was a circumference of a circle, what would be the imaginary circle's area?

4 π 3 π \frac{4\pi^{3}}{\sqrt{\pi}} 1 π \frac{1}{\sqrt{\pi}} 9 π 3 4 \frac{9\pi^{3}}{4} π 5 π \frac{\sqrt{\pi^{5}}}{\sqrt{\pi}}

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

1 solution

Kaizen Cyrus
Jan 27, 2019

Let D D be the disk and P P be the circular path.

The disk had an area of 1 1 squared unit. We can figure out the disk's circumference with this information.

D A = 1 π r 2 = 1 r 2 = 1 π r = 1 π or 1 π or π π \begin{aligned} D_{A} &=1 \\ πr^{2} &=1 \\ r^{2} &= \frac{1}{π} \\ r &= \sqrt{\frac{1}{π}} \small \text{or} \frac{\sqrt{1}}{\sqrt{π}} \small \text{or} \frac{\sqrt{π}}{π} \end{aligned}

With the radius given, we can solve for D C D_{C} or the disk's circumference.

D C = 2 π r = 2 π ( π π ) = 2 π \begin{aligned} D_{C} &= 2πr \\ &= 2π(\frac{\sqrt{π}}{π}) \\ &= 2\sqrt{π} \end{aligned}

It was said that P C P_{C} or the path's length is π π times D C D_{C} .

P C = D C π = ( 2 π ) π = 2 π 3 \begin{aligned} P_{C} &= D_{C}π \\ &= (2\sqrt{π})π \\ &= 2\sqrt{π^{3}} \end{aligned}

We turn P P into a circle. If the path's length is P C P_{C} or the circle's circumference, we can now get P A P_{A} or the area of the circle.

2 π r = 2 π 3 r = 2 π 3 2 π r = π \begin{aligned} 2πr &= 2\sqrt{π^{3}} \\ r &= \frac{2\sqrt{π^{3}}}{2π} \\ r &= \sqrt{π} \end{aligned}

P A = π r 2 = π ( π ) 2 = π 2 \begin{aligned} P_{A} &= πr^{2} \\ &= π(\sqrt{π})^{2} \\ &= π^{2} \end{aligned}

So the area of the imaginary circle is π 2 π^{2} which is also equal to π 5 π \frac{\sqrt{π^{5}}}{\sqrt{π}} .

π 2 π π = π 2 π π = π 2 π 1 2 π 1 2 = π 5 2 π 1 2 = π 5 π π^{2} \cdot \frac{\sqrt{π}}{\sqrt{π}} = \frac{π^{2}\cdot\sqrt{π}}{\sqrt{π}} = \frac{π^{2}\cdotπ^{\frac{1}{2}}}{π^{\frac{1}{2}}} = \frac{π^{\frac{5}{2}}}{π^{\frac{1}{2}}} = \boxed{\frac{\sqrt{π^{5}}}{\sqrt{π}}}

Since π π \frac{\sqrt{π}}{\sqrt{π}} is equals to 1 1 , we don't actually change the value when it's multiplied to π 2 π^{2} .

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...