A string (A) hanging from the ceiling has a 1 kg mass attached to it and hanging below this mass is string (B) with a 2 kg mass attached. Both of the strings are massless.

Question

How do I calculate the tension in Cord B?

Answer 1

Schematically, it looks like this (turned 90 degrees)

Ceiling|-->-A-<---1kg--->-B-<----2kg

The only mass string B is supporting is the 2kg mass. So the tension in string B is
Tension
=mg
=2kg * g
=2*9.8 N
=19.6 N.