( $g=10 ms ^{-2}$ લો.)
\(PE = KE\)
\(mg \left( H +\frac{ H }{2}\right)=\frac{1}{2} kx ^{2}\left( x =\frac{ H }{2}\right)\)
\(0.100 \times 10 \times \frac{3}{2}(0.10)=\frac{1}{2} k (0.05 \times 0.05)\)
\(k =\frac{3 \times 0.10}{0.05 \times 0.05}\)
\(=\frac{3 \times 1000}{25}=120\, N / m\)