Experiments using "optical tweezers" measure the elasticity of individual dna molecules. for small enough changes in length, the elasticity has the same form as that of a spring. a dna molecule is anchored at one end, then a force of 1.5 nn (1.5×10−9n) pulls on the other end, causing the molecule to stretch by 5.0nm (5.0×10−9m). what is the spring constant of that dna molecule?