The Equation Describing the Position of an Object Undergoing Simple $x = ( 5.0 \mathrm {~cm} ) \cos ( 10 \pi t - \pi / 2 )$

Multiple Choice

The equation describing the position of an object undergoing simple harmonic motion is $x = ( 5.0 \mathrm {~cm} ) \cos ( 10 \pi t - \pi / 2 )$ , where t is in seconds. The velocity of the object at t = 0.20 seconds is

A) zero.
B) 13 cm/s.
C) -5.0 cm/s.
D) -160 cm/s.