Remark
You can't really tell. Somewhere you have to declare which way is up (or down)
You also have to declare whether up is plus or minus. Without that declaration, a velocity like 13 feet per second is meaningless.
So if you know something about up or down or plus or minus, please state it.
Answer:
A roller coaster is a machine in which rides are taken for amusement sometimes in the form of elevated railroad track fixed with turns, slanted slopes, and diversions.
Speed of Roller coster =13 feet per seconds
When there will be elevation ,the speed will go down and when there is slanting up, speed of Roller coster will increase, and when there is slanting down, speed of Roller coster will decrease ,and when there will be diversion speed will surely decrease.
So,it totally depends on the position of the roller coster on the track ,whether you are moving up or down.
