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  1. Hello there! Please visit my channel and have a look 🙂 I do update it every day or so. I teach lessons and I try my best to make them as easy to understand as possible. If you would like to request a topic, either message me or just comment on my videos. I would get them up within a two days. Thanks.

  2. You don't actually need to transform into C's frame of reference for this problem. From A's frame:

    u' = (u – v) / (1 – uv/c^2)
    Let's define terms:
    v is the speed of C as seen by A.
    u is the speed of B as seen by A.
    u' is the speed of B as seen by C.

    The key thing to note here is that v = u'. This is because A sees C travelling at some velocity, so C sees A travelling at the same velocity but in the opposite direction. Because C sees A and B at the same speeds but opposite directions, then C sees B the same way A sees C.

    Plugging in that u' = v:
    v = (u – v) / (1 – uv/c^2)

    Now we plug in the numbers:
    v = (0.8c – v) / (1 – 0.8v/c)

    Doing simple algebra, we find that v = 0.5c

  3. Mr. Khan, at the beginning of this video you said A is moving with constant velocity. But didn't say with respect to which frame.

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