(a) An object with a constant acceleration but zero velocity is possible. For example, when an object is just released from a height, then it is being acted upon by a constant acceleration of `9.8 m//s^(2)` (called acceleration due to gravity) but its initial velocity is zero.
(b) An object moving in a certain direction with an acceleration in the perpendicular direction is possible. For example, when an object is moving with uniform motion in a circle, then the motion of the object at any instant of time is along tangent to the circle at that instant but the (centripetal) acceleration is along the radius of the circle (which is perpendicular to the direction of motion along the tangent).
