Answer:
[tex]20.8cm[/tex]
Explanation:
According to hooks law "provide the elastic limit of an elastic material is not exceeded the extension e is directly proportional to the applied force F"
[tex]F= ke[/tex]
where F= applied force
k= spring constant
e= extension
Given data
length of string l = 16cm
extension e = 20-16= 4cm
applied force = 5N
we need t o first calculate the spring constant k
apply the formula
[tex]F= ke[/tex]
[tex]5=k*4\\k= \frac{5}{4} \\k= 1.25N/cm[/tex]
we can now calculate the extension of the string when supporting a 6N weight
[tex]F= ke\\6=1.25*e\\e= \frac{6}{1.25} \\e= 4.8cm[/tex]
The length of the string when supporting a 6N weight is
[tex]= length+ extension\\= 16+4.8\\= 20.8cm[/tex]
COMMENT :According to the analysis an extra weight of 1N will cause add 0.8cm to the length of the string
