Relative Velocity Example

We now consider how observations made in different frames of reference are related to each other. For example, consider two trains approaching one another, each with a constant speed of 80 km/h with respect to the Earth. Observers on the Earth beside the tracks will measure 80 km/h or the speed of each train. Observers on either of the trains (a different reference frame) will measure a speed of 160 km/h for the other train approaching them.

You will use vectors to help solve these relative velocity problems. It is imperative that you draw a diagram and label that diagram carefully. One common practice is to label each velocity vector with two subscripts: the first refers to the object, the second refers to the reference frame (i.e. the velocity of the first train relative to the second in our illustration above would be .

Select the play button to begin the example, and then use the solve button to view the solution and use the navigation buttons to pause/stop the example. View the presentation as often as you would like, and take notes as you follow along. Be sure to set your volume at a reasonable level before you begin.

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Take a look at the example problems in your textbook for some more problem solving. In section 3-8 Relative Velocity. Also, complete problems 41-51 odd in "Chapter 3, Problems" at the end of the chapter.