Question

A sprail spring balance 25cm long when 5N hangs on it and 30com, the weigh is 10N. What is the length of the spring if the weigh is 2N. Assume hookie's law is obey

Answer 1

No answer

Answer 2

let L = initial length with no weight
then
extension = ex = x - L
and
F = k * ex = k (x - L)
5 = k * (25-L) = 25 k - kL
10 = k (30-L) = 30 k - kL
-5 = -5 k
k = 1
which you could see by inspection anyway
then
10 = 30 - L
L = 20 = unextended length
2 Newtons = 1 * extension
extension = 2 cm
L = 20
so length with 2 N = 22 cm

Answer 3

F=kx, so you want L when F=2.
(30-25)/(10-5) = (25-L)/(5-2)
L = 22