Motion-related Problems

Motion with constant velocity
Let s = distance, v = speed, t = time
$s = vt$
 

Motion with water/air current
x = speed of boat/airplane in still water/air
y = velocity of water/air current

$v = x + y$   ←   net velocity when moving with the current

$v = x - y$   ←   net velocity when moving against the current
 

Motion around a closed loop
Starting from the same point at the same time, the moment that they are together...
$d_\text{faster} + d_\text{slower} = 1 ~ \text{loop}$   ←   moving in opposite directions

$d_\text{faster} - d_\text{slower} = 1 ~ \text{loop}$   ←   moving in the same direction