A particle's velocity is given by vy(t) = −atj, where a = 0.765 m/s2 is a constant. (b) Find the particle's velocity at
t = 0,

t = 19.0 s,
and
t = 5.20 min.
(Express your answer in vector form.)
(c) Find the particle's speed at
t = 0,

t = 19.0 s,
and
t = 5.20 min.