The path taken by light traveling from one point to another is such that the time of travel is a minimum. This is called

When the force acting on an object points at least partially in the direction of the motion the work done is considered to be negative

You are traveling in a car going at a constant speed of 100km/h down a long, straight highway. you pass another car going in the same direction which is traveling at a constant speed of 80km/h. as measured from your car's reference frame this other car is traveling at −20km/h. what is the acceleration of your car as measured from the other car's reference frame? what is the acceleration of the other car as measured from your car's reference frame?

If a star is moving toward earth, it is