A system consists of two identical cubes, each of mass m, linked together by the compressed weightless spring of stiffness `ϰ` (figure). The cubes are also connected by a thread which is burned through at a certain moment. Find:
(a) at what values of `Deltal`, the initial compression of the spring, the lower cube will bounce up after the thread has been burned through:
(b) to what height h the centre of gravity of this system will rise if the initial compression of the spring `Deltal=7mg//ϰ`.

Options

A. `(2 mg)/(k)`
B. `(3 mg)/(k)`
C. `(3 mg)/(2 k)`
D. `(6 mg)/(k)`

Answer

B