>How fast is a fly going at 10 kph from the back to the front of a car moving at 100 kph?<
Is this a catch question?
I assume the car is moving forward? I assume the observer is not in the car? And is stationary?
Etc, etc?
Then from the point of view of the fly it is stationary.
From the point of view of the car it is moving forward at 10 kph.
From the point of view of a standing observer, it is moving at 110 kph.
If you wish to be really, really precise, relativistically speaking, then you need to appeal to the Fitzgerald contraction, which at such velocities is too nearly negligible for most everyday purposes, for me to wish to trouble to express it in this medium.
Will you be elaborating on the intent of the question?
And Georg, yes, you are right. One needs to be careful about the capitalisation and the context. For example, mps could be metres or miles per second. It can be very misleading and very irritating. However, it does one's blood pressure no good to get impatient. Rather just think peaceful thoughts and make sure you have the context right!
