Explain what happens in a series circuit if one of the light bulbs stop shining?

In a series circuit, there's only one path for current, so the current
for each bulb has to go through all of them. 

If one bulb stops shining ... either because it burned out, or because
somebody unscrewed it and ran away with it ... then no current can flow
through the place where that bulb used to be, and they ALL go out. 

This is the main reason why the lights in your house are NOT in series. 
There are a lot of other reasons.

4. 50x10= 500m/s 5. 52m/s