Question

In the given diagram, when a weight of 100 g is hung from the spring, its length is 9 cm. When a weight of 150 g is hung from it, its length is 11 cm. What is the length of the spring when there's no weight hanging from it ?

• A. 2 cm
• B. 4 cm
• C. 5 cm
• D. 7 cm

Answer 1

The correct option is C 5 cm

From Hooke's Law

$F=-K\ast x$

Also

$F=m\ast g$

when 100g is hung,length is 9

$mg=-Kx$

$100g=K(9-l)$

similarly for second one

$150g=K(11-l)$

By equating both we will get the following equations

$\frac{9-l}{11-l}=\frac{100}{150}$

$l=5cm$