Just a question

In this setup, when a filament within any one bulb blows out, it creates an open circuit in the wiring. As we mentioned earlier, when a circuit is incomplete, or open, electricity fails to pass through any of the wire, causing all the lights to go out

beta is electron from nucleus

something from nucleus has changed, but charge must be same for cons of charge

one person pulls 90n one way and the other has 100n pulling the other way.

so the net force = 90 - 100 = -10n,

or the ans can be 10n if the picture shows -90n and 100n instead.