The Period of an Oscillating Weight on a Spring in an Inertial

Multiple Choice

The period of an oscillating weight on a spring in an inertial frame of reference is 2.5 s.What would be its speed if it were to move by an observer who measures its period as 3.4 s? (c = 3.00 × 10⁸ m/s)

A) 1.5 × l0⁸ m/s
B) 2.0 × 10⁸ m/s
C) 2.8 × l0⁸ m/s
D) 6.8 × 10⁷ m/s
E) ​1.3 × 10⁸ m/s