Solve
-A Coil of Wire Rotating in a Magnetic Field $= 20 \sin \left( \frac { \pi t } { 4 } - \frac { \pi } { 2 } \right)$

Multiple Choice

Solve.
-A coil of wire rotating in a magnetic field induces a voltage given by e $= 20 \sin \left( \frac { \pi t } { 4 } - \frac { \pi } { 2 } \right)$ , where $t$ is time in seconds. Find the smallest positive time to produce a voltage of $10 \sqrt { 2 }$ . Round values to the nearest hundredth.

A) $3 \mathrm { sec }$
B) $2.8 \mathrm { sec }$
C) $2.8 \pi \mathrm { sec }$
D) $3 \pi \mathrm { sec }$