centripetal acceleration always points towards the center of the circular path and velocity of object in circular motion always points towards the tangent on the the circle in this way centripetal acceleration and velocity are perpendicular to each other and the dot product of perpendicular vectors is always zero,
therefore v•a=vacosα...........(1)
here α is angle between centripetal acceleration and velocity which is 90
therfore,
From equation (1)
v.a= vacos90
v.a=vax0..............(because cos90=0)
v.a=0 m^2
centripetal acceleration vector points towards center it means it point towards inwards direction, so it lies along the radius vector,and radius vector points towards outward direction of the circle in this way centripetal acceleration and radius vector are in exact opposite direction so angle between them is 180 degree,
therefore r x a = rasin180
rxa=rax0 (because sin180=0)
rxa=0m^2/s^2 .