You have a light spring which obeys Hooke's law. This spring stretches $2\mathrm{.}42$ cm vertically when a $2\mathrm{.}50$ kg object is suspended from it$.$ Determine the following. $($a$)$ the force constant of the spring $($in N $/$ m $)$ N $/$ m $($b$)$ the distance $($in cm $)$ the spring stretches if you replace the $2\mathrm{.}50$ kg object with a $1\mathrm{.}25$ kg object cm $($c$)$ the amount of work $($in J$)$ an external agent must do to stretch the spring $6\mathrm{.}50$ cm from its unstretched position J