A Mass Attached to a Spring Moves Horizontally on a Frictionless

Short Answer

A mass attached to a spring moves horizontally on a frictionless track. Its displacement from the rest position at time $t$ is given by $x=0.3 \cos (7 \pi t)$ . If displacement is measured in inches and time is measured in inches, when is the mass 0.15 inches from the rest position? Restrict your answer(s) to $0<t<\frac{2}{7}$ , and round to 3 decimal places.