Answer: 75 mph
Explanation:
The Relative Speed for a mobile is equal to the diference between the object and the observer:
Relative Speed (Rs) = Object's Velocity - Observer's Velocity
Thinking on those terms, we would need to have a universal observer to do any understandable measurement on daily basics. This is why we all use earth as a Static Observer for every measurement we do everyday.
Using Earth as an observer, the Velocity for the Patrolman is:
Patrolman Velocity (Vp) = 60 mph
Because the radar gun does measure the Relative Speed for the object, which is 135 mph, we need to work with the equation to find the Velocity using Earth as a reference.
Object's Relative Velocity = Object's Velocity - Patrolman's Velocity
Object's Velocity = Object's Relative Velocity + Patrolman's Velocity
We need to keep in mind, the Patrolman is going on the opposite direction. Because of this the sign for his velocity should be negative.
Object's Velocity = 135 mph + ( -60 mph)
Object's Velocity = 135 mph - 60 mph
Object's Velocity = 75 mph
