Clark Kent

[kuiperbelt]

Superman flew due east from the Shetland Islands (Latitude 60 degrees North, Longitude 1.2 degrees West) until he was back where he started. The next day he flew do east from a capital city. Although he flew at the same speed the trip took twice as long. Where might he have been?

[Old_Geezer]

Off to get a birthday present for Clark ?

[bhg481]

Quito, Ecuador. The trip is twice as long so needs to be at latitude 0.

[bhg481]

Just to expand on the answer, the radius of a sphere is proportional to cos(latitude); the circumference, of course, is proportional to the radius.
Cos(60) = 0.5, so we need a latitude such that cos(latitude)=1 ie, the equator.

[ZebuSanctuary]

// Quito, Ecuador //

Since Quito lies on a latitude 0.18° South, proffered is Pontianak.

Albeit not the capital of Indonesia, it is recognised as the capital city of the province West Kalimantan which is located on the equator (0.0°).

Hint; r = RCosφ

Where R is Earthradius, φ represents latitude° and r signifies the radius of a line of latitude.

[Etch]

Could be any capital city on Earth. What has been overlooked is that the time taken depends not just on the latitude but also the altitude (height above sea level) at which the flight takes place. Superman is able to survive for long periods in space so being above the breathable atmosphere isn't a problem for him and altitudes several times the Earth's radius are perfectly feasible.

[ClareTG0ld]

On the other hand, if Superman took a detour up to space, he wouldn't be flying "due east", but "due east and a bit up".

[Old_Geezer]

He's up up & away anyway.