Joshua has built a remote-controlled merry-go-round of radius meters and he noticed that it had a rotational frequency of when he stood on it. He initially stood at , 2 meters from (the closest point on the circumference of his merry-go-round) as shown above. He then walked a straight path to , passing through , and used his remote to activate the merry-go-round. Joshua experienced a total displacement of meters after standing at the same position for exactly 3 minutes, shutting down the merry-go-round, and walking back to . Let the distance between and be . Find .
Note: This image is not drawn to scale.
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.
We are given that the merry-go-round has a radius of 4 meters. Joshua initially stands 2 meters away from the nearest point on his merry-go-round, and he experiences a total displacement of π 5 4 8 π − 3 meters after walking through point B to point 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 second radians when he stands on it.
From this, we can set up a linear equation to solve for the distance between B and C . If we let the distance between B and C be s , the distance from the center of the merry-go-round to point C is 4 − s .
Hence, Joshua experienced a displacement of 2 π ( 4 − s ) revs meters × 9 0 revs = 1 8 0 π ( 4 − s ) meters from the rotations of his merry-go-round. In his path, Joshua walked from B to C and back, covering 2 s meters, and from A to B and back, covering 4 meters.
Since his total displacement is π 5 4 8 π − 3 , we see that 1 8 0 π ( 4 − s ) + 2 s + 4 = π 5 4 8 π − 3 ⟹ ( 2 − 1 8 0 π ) s = π 5 4 8 π − 3 − 4 − 7 2 0 π ⟹ s = 2 − 1 8 0 π π 5 4 8 π − 3 − π 4 π − 7 2 0 π = 2 − 1 8 0 π π 5 4 4 π − 3 − 7 2 0 π ∴ s ≈ 3 . 0 5 0 4 7 ⟹ ⌊ s ⌋ = 3 .