Answer:
.
Step-by-step explanation:
Note the unit conversion: standard unit of distance should be meters, not centimeters.
Divide the restoring force
by the displacement
of the spring to find the spring constant:
.
When the displacement of the spring is
, the elastic potential energy stored in this spring would be
. Subtract the initial value of elastic potential energy from the new one to find the energy required:
.
In other words, the energy required to stretch the spring would be
.