we know force=ma.if the object is at rest no force is applied on it.f=0.if the object moves with uniform velocity then acceleration=0.f=ma=m X 0=0.both the forces are 0.then does it mean that the state of rest and of uniform motion is same. if so,what happens to the force applied to move the body in uniform velocity???

First of all, is the object is at rest, we cannot conclude that the force applied on it is zero.
We may say that the net force is zero over it (Eg. consider the motion of a body at highest point of the projection where the object is rest with respect to vertical direction but a force W is acting over it). But for the uniform motion, velocity is constant. Thus, ∂v/∂t = a = 0. If the acceleration acts in a direction perpendicular to that of velocity, then also the velocity remains constant (Case of uniform circular motion). So we see that there is a diff. btw the state of rest and state of uniform motion.

State of rest and state of uniform motion are same.  In a way, state of rest is a special case where velocity is zero.  There is no difference in observation made from a reference frame at rest to the observation made by another reference frame moving with constant velocity.

When a body is moving with uniform velocity that means net force on the body is zero.  For example if a body is being pulled by a force F and the body is in uniform motion, that means, the friction force acting on the body is equal to F and hence net force is zero.