Question

In the figure three identical springs are shown. From spring $A$, a mass of $4kg$ is hung and spring shows elongation of $1cm$. But when a weight of $6kg$ is hung on $B$, the hook descends through

• A. 1 cm
• B. 2 cm
• C. 3 cm
• D. 4 cm

Answer 1

Answer: (C)

As, $x=\frac{r}{k}$
If spring constant is $k$ for the first case, it is $\frac{k}{2}$ for second case.
For first case, $1=\frac{4}{k}$ ... (i)
For second case, $x^{\prime }=\frac{6}{k/2}=\frac{12}{k}$ ... (ii)
Dividing Eq. (ii) by Eq. (i), we get
$x^{\prime }=\frac{12/k}{4/k}=3cm$