Final answer:
The period T of the box attached to two side-by-side springs is described by the formula T = 2π√(m/keff), where keff is the sum of the spring constants (k1 + k2) and m is the mass of the box.
Step-by-step explanation:
To determine the expression that describes the period T of the motion of a box attached to two springs side by side, we can consider the springs' force constants k1 and k2, which are given as 1 and 2 respectively.
Since the springs are attached side by side, their effective spring constant keff is the sum of their individual constants: keff = k1 + k2. Thence, the effective force constant is keff = 1 + 2 = 3.
The period T for a simple harmonic oscillator such as this system is given by the formula: T = 2π√(m/keff), where m is the mass of the box. Replace keff with the sum of the spring constants to find the period of the box.