The potential energy (in joule) of a small block
of mass 2 kg moving in the x-y plane is given by
U = 6x + 8y
where the position coordinates x and y are
measured in metre. If the block is at rest at point
(6 m, 4m) at time t = 0, it will cross the y-axis at
time t equal to -
(A) 1 s (B) 2 s (C) 3 s (D) 4 s