Find the magnitude of a particle's acceleration vector at t = 0 for a particle moving with position vector r of t equals components the cosine of t, t cubed

Question

Find the magnitude of a particle's acceleration vector at t = 0 for a particle moving with position vector  

A	1
B	0
C	2
D	3

Answer 1

v(t) = r'(t) = <-sin(t), 3t²>

a(t) = v'(t) = <-cos(t), 6t>;

a(0) = <-1,0>

Ia(0)I = √(-1)² + 0² = 1

Answer is A