physics
posted by sagor .
A light spring with spring constant 1 200 N/m is hung from
an elevated support. From its lower end hangs a second
light spring, which has spring constant 1 800 N/m. An
object of mass 1.50 kg is hung at rest from the lower end of
the second spring. (a) Find the total extension distance of
the pair of springs. (b) Find the effective spring constant
of the pair of springs as a system. We describe these springs
as in series.

Springs in series add like resistors in parallel.
1/Keff = 1/K1 + 1/K2
= 1/1200 + 1/1800
= 5/3600 = 1/720
Keff = 720 N/m
Is the effective spring constant of the pair of springs in series.
Extension = M*g/Keff