In a particular reference frame, an electron has a velocity of c/2 in the x direction and a photon has a velocity of c in the y direction. According to classical physics, what is the relative speed of the electron and the photon? (i.e. What speed does the electron see the photon traveling at?)

According to relativity, what is the relative speed of the electron and photon? (Show two ways to get the answer)

In the frame S, two electrons approach each other, each having a speed u = c/2. What is the relative speed of the two electrons? (Hint: Transform to a frame where one electron is stationary)

You are traveling at 50 m/s toward a source emitting 200 Hz waves traveling at 100 m/s. What is the frequency of the wave observed by you?

A 200 Hz wave source is traveling toward you at 50 m/s. If the wave speed is 100 m/s, what frequency of do you observe?