For a Person at Rest, the Velocity V (In Liters $0.9 \sin \frac { \pi t } { 7 }$

Multiple Choice

For a person at rest, the velocity v (in liters per second) of air flow into and out of the lungs during a respiratory cycle is given by $0.9 \sin \frac { \pi t } { 7 }$ , where t is the time in seconds. Inhalation occurs when $v > 0$ and exhalation occurs when $v < 0$ . Find the time for one full respiratory cycle.

A) $14 \pi$ seconds
B) $\pi$ seconds
C) 14 seconds
D) $2 \pi$ seconds
E) 7 seconds