Physics Velocity Question
posted by Jennifer .
The equation for the displacement in meters of an object moving in SHM is x(t) = 1.50 cos (4.20t) where t is in seconds. (a) What is the maximum speed of the object? (b) At what time does it first reach the maximum speed?
I already got 6.3m/s for A and I got B wrong. I thought it was 1.12 s

v =  1.50 (4.20) sin 4.2 t
the maximum speed is when the sine function is +1 or 1
since the sign is negative the sine function reaches 1 first.
vmax = max speed = 1.5*4.2 = 6.3 m/s
this is when 4.2 t is pi/2 radians
t = pi/8.4 = .374 s