Q. Natural length of a spring is $60\ cm$, and its spring constant is $4000\ N/m$. A mass of $20\ kg$ is hung from it. The extension produced in the spring is, (Take $g = 9.8\ m/s^{2})$
A) $4.9\ cm$
B) $0.49\ cm$
C) $9.4\ cm$
D) $0.94\ cm$
Explanation
(a) If $x$ is the extension produced in spring
$F = kx \Rightarrow x = \frac{F}{k} = \frac{mg}{k} = \frac{20 \times 9.8}{4000} = 4.9\ cm$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.