Question

Natural length of a spring is $60cm$ and its spring constant is $4000N/m$. A mass of $20kg$ is hung from it. The extension produced in the spring is (take g = $9.8m/s^2$):

• A. $4.9cm$
• B. $0.49cm$
• C. $9.4cm$
• D. $0.94cm$

Answer 1

The correct option is A $4.9cm$

Given, $l=60cm=60\times {10}^{-2}m$
$m=20kg,k=4000N/m$
The weight hung from the spring $=mg=20\times 9.8=196N$
Let $x$ be the extension produced in spring.
Now, force applied by the spring = downward force on the spring
$\therefore kx=mg\Rightarrow x=\frac{mg}{k}$
or, $x=\frac{20\times 9.8}{4000}=0.049m=4.9cm$