A mass on a spring vibrates horizontally on a smooth level surface (see the figure). Its equation of motion is x(t) = 4 cos t, where t is in seconds and x is in centimeters.
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a. Find the velocity and acceleration at time t.
b. Find the position, velocity, and acceleration of the mass at time t = 5 π/6.
c. In what direction is it moving at that time?