Solve the Problem $s ( t ) = - 3 \cos 7 \pi t$

Multiple Choice

Solve the problem.
-The position of a weight attached to a spring is $s ( t ) = - 3 \cos 7 \pi t$ inches after $t$ seconds. When does the weight first reach its maximum height?

A) After $\frac { \pi } { 7 } \mathrm { sec }$
B) After $\frac { 1 } { 7 } \mathrm { sec }$
C) After $\frac { 7 } { \pi } \mathrm { sec }$
D) After $\frac { 7 } { 4 } \mathrm { sec }$