Conversation so far:
what is the purpose of a roller coaster
A roller coaster is a type of amusement ride that employs a form of elevated railroad track designed with tight turns, steep slopes, and sometimes inversions.
where is the tallest roller coaster
Kingda Ka with a 418-Foot Drop is the tallest roller coaster.

Question: How long is the ride
Self-contained rewrite: How long is the kingda ka roller coaster