Answer:
if you stretch a spring with k = 2, with a force of 4N, the extension will be 2m. the work done by us here is 4x2=8J. in other words, the energy transferred to the spring is 8J. but, the stored energy in the spring equals 1/2x2x2^2=4J (which is half of the work done by us in stretching it).
The simplest answer would be "acceleration due to gravity."
The exact value of this acceleration changes depending on which planet your on (for example).
A. hot is the correct answer.
Hope it helps!
