at what rate will heat be transferred between it ends?

Question

A cylinderical shaped metal rod is used to conduct heat. When the temperature at one end is 100 degree Celsius and at the other end is 20 degree Celsius, heat is transferred at a rate of 16 J/s. The rod is then stretched uniformly to twice its original length. If again it has ends at 100 degree Celsius and 20 degree Celsius, at what rate will heat be transferred between it ends?

The answers that are given to me are:
4 J/s
8 J/s
32 J/s
2 J/s
64 J/s
16 J/s
1 J/s

Answer 1

The formula for thermal conduction is ∆Q/∆t = k*A*∆T/∆x. You are given ∆Q/∆t, ∆T and ∆x. so solve for k*A; Then use this constant in the equation again to get ∆Q. More simply, you can see that heat transfer rate is inversely proportional to length. Since that is the only thing changed, and it stretched to twice its length, the heat transfer rate will be cut in half.

Answer 2

It is 4 J/s.