Concept:
According to Hooke's law, extension is directly proportional to the applied force within the elastic limit.
\[
\Delta L \propto F
\]
Step 1: Determine extension produced by 150 N force.
Given,
\[
50N \rightarrow 0.5\text{ cm}
\]
Therefore,
\[
150N \rightarrow \frac{150}{50}\times0.5
\]
\[
=1.5\text{ cm}
\]
Step 2: Calculate final length.
Initial length
\[
L_0=149\text{ cm}
\]
Final length
\[
L=149+1.5
\]
\[
L=150.5\text{ cm}
\]
Hence,
\[
\boxed{150.5\text{ cm}}
\]