In order to move body along with the sprite in cocos2d with box2d,you no need to worry about. Just take a look to this:-

PhysicsSprite* sprite = (PhysicsSprite*)body->GetUserData();

 CGPoint target;

 //set target for the body

 target = CGPointMake(0,size.height);

 int speed=10;

 //convert target point into toMeters

 b2Vec2 destination = [self toMeters:target];

 //calculate distance between destination vector and a body current position

 b2Vec2 toTarget = destination - body->GetPosition();

 toTarget.x = toTarget.x/toTarget.Length()*speed;

 toTarget.y = toTarget.y/toTarget.Length()*speed;

 //Move body to a targeted position using impulse 

 body->ApplyLinearImpulse(toTarget,body->GetWorldCenter());

 //calculate angle 

 float val = 0.0174532925199432957f;

 float ax = destination.x-body->GetPosition().x;

 float ay = destination.y-body->GetPosition().y;

 float angle = atan(ay/ax);

 //convert angle into radian by multiplying it with val

 angle=angle*val;

 //finally transform body along with the angle

 body->SetTransform(body->GetPosition(), angle);

Hope this one will be helpful for you,enjoy code :)