object pass through even when having rigidbody

i have attached rigidbody component to a player car and to enemy car. it like a simple 2d car game, where player has to move right or left to avoid collision. when the game starts and if i dont give any movement to the player, even when he has rigidbody and also the script on him, the enemy cars just pass through him and dont destroy. but when i give a small movement to right or left then if any enemy car touches him the collision happens, it simply means the player is acting just like a texture until when i give him a movement then he starts acting as an object. it is my asumption right that the rigidbody of the player is inactive till i give a motion or a inital input to it? please help me solve this problem.