Question

The following figure shows three identical springs $A,B,C$. When a 4 kg weight is hung on $A$, it descends by $1$ cm. When a $6$ kg weight is hung on $C$, it will descend by

• A. 1.5 cm
• B. 3.0 cm
• C. 4.5 cm
• D. 6.0 cm

Answer 1

The correct option is B 3.0 cm

The spring constant can be found out by
$k=\frac{F}{x}=\frac{4\times 10}{0.01}=4000N/m$
Now, when two springs are connected in series, their equivalent constant is
$\frac{1}{k_{eq}}=\frac{1}{4000}+\frac{1}{4000}$
$k_{eq}=2000N/m$
Therefore, mass of 6 kg will descend by
$x=\frac{6\times 10}{2000}=0.03m=3cm$
Option B is thus correct.