Imagine that a person is holding a basket of baseballs, and is throwing them at you, a helpless person without a baseball glove, with a speed of 10m/s, every two seconds. Assume you are a distance of 50m away.
A. How long will it take until you get hit with the first ball?
B. How often will you get pelted with baseball?
Now, Imagine that the attacker is moving towards you with a speed of 5m/s, but can only throw the baseballs with a speed of 10m/s (from your reference frame). The first ball is thrown when the person is 50m from you.
A. How long will it take until you get hit with the first ball?
B. How often will you get pelted with baseballs?
Finally, you get your wits about you and start running away from the mad attacker, at a speed of 5m/s. The attacker was tired and stopped to catch his breath, but started throwing the baseballs again when you are a distance of 50m away from him.
A. How long will it take until you get hit with the first ball?
B. How often will you get pelted with baseballs?