Fill in the blanks:
$1.$ In $SHM$,......... quantities are always positive.
$2.$ $A$ periodic motion that obeys the force law ......... is only a simple harmonic motion.
$3.$ $A$ $SHO$ with a periodic time of $2 \ s$ starts its oscillation from the lower end of its path of motion; its phase will be .......... at time $t = 2 \ s$.

(N/A) $1.$ In $SHM$,the magnitude of force and acceleration are always positive.
$2.$ $A$ periodic motion that obeys the force law $F = -kx$ is a simple harmonic motion.
$3.$ Given $T = 2 \ s$,initial position is at the lower end (extreme position),so initial phase $\phi = \frac{3\pi}{2}$.
Phase $\theta = \frac{2\pi t}{T} + \phi = \frac{2\pi}{2} \times 2 + \frac{3\pi}{2} = 2\pi + \frac{3\pi}{2} = \frac{7\pi}{2} \ rad$.