Joshua's Merry-go-round

Joshua has built a remote-controlled merry-go-round of radius 4 4 meters and he noticed that it had a rotational frequency of ω = π radians second \omega = \pi\dfrac{\text{radians}}{\text{second}} when he stood on it. He initially stood at A A , 2 meters from B B (the closest point on the circumference of his merry-go-round) as shown above. He then walked a straight path to C C , passing through B B , and used his remote to activate the merry-go-round. Joshua experienced a total displacement of 548 π 3 π \dfrac{548\pi-3}{\pi} meters after standing at the same position for exactly 3 minutes, shutting down the merry-go-round, and walking back to A A . Let the distance between B B and C C be s s . Find s \lfloor{s}\rfloor .

Note: This image is not drawn to scale.


The answer is 3.

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1 solution

Akeel Howell
Mar 15, 2017

We are given that the merry-go-round has a radius of 4 4 meters. Joshua initially stands 2 2 meters away from the nearest point on his merry-go-round, and he experiences a total displacement of 548 π 3 π \dfrac{548\pi-3}{\pi} meters after walking through point B B to point C C on the merry-go-ground and standing there for exactly 3 minutes while it was being operated before walking back to his initial position. We are also given that the merry-go-round has a rotational frequency of π radians second \pi \dfrac{\text{radians}}{\text{second}} when he stands on it.

From this, we can set up a linear equation to solve for the distance between B B and C C . If we let the distance between B B and C C be s s , the distance from the center of the merry-go-round to point C C is 4 s 4-s .

Hence, Joshua experienced a displacement of 2 π ( 4 s ) meters revs × 90 revs = 180 π ( 4 s ) meters 2\pi(4-s) \dfrac{\text{meters}}{\text{revs}} \times 90 \text{ revs} = 180\pi(4-s) \text{ meters} from the rotations of his merry-go-round. In his path, Joshua walked from B B to C C and back, covering 2 s 2s meters, and from A A to B B and back, covering 4 4 meters.

Since his total displacement is 548 π 3 π \dfrac{548\pi-3}{\pi} , we see that 180 π ( 4 s ) + 2 s + 4 = 548 π 3 π ( 2 180 π ) s = 548 π 3 π 4 720 π s = 548 π 3 π 4 π π 720 π 2 180 π = 544 π 3 π 720 π 2 180 π s 3.05047 s = 3 180\pi(4-s)+2s+4 = \dfrac{548\pi-3}{\pi} \\ \implies (2-180\pi)s = \dfrac{548\pi-3}{\pi}-4-720\pi \implies s = \dfrac{\dfrac{548\pi-3}{\pi}-\dfrac{4\pi}{\pi}-720\pi}{2-180\pi} = \dfrac{\dfrac{544\pi-3}{\pi}-720\pi}{2-180\pi} \\ \therefore s \approx 3.05047 \implies \lfloor {s} \rfloor = \space \boxed{3} .

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