$5.$ A very light ideal spring stretches by $21\mathrm{.}0$ cm when it is used to hang a $135-N$ object. What is the weight of a piece of electronic equipment that would stretch the spring by $44\mathrm{.}9$ cm if you hung the equipment using the spring?

A$)289$ N

B$)63$ N

C$)176$ N

D$)405$ N

An object attached to a spring is pulled across a horizontal frictionless surface. If the spring constant is $45\frac{N}{m}$ and the spring is stretched by $0\mathrm{.}88$ m when the object is accelerating at $1\mathrm{.}4\frac{m}{s^2},$ what is the mass of the object?

A$)28$ kg

B$)24$ kg

C$)31$ kg

D$)36$ kg