Research has shown that modifying the aspect of the virtual hand in immersive virtual reality can convey objects properties to users. Whether we can achieve the same results in augmented reality is still to be determined since the user's real hand is visible through the headset. Although displaying a virtual hand in augmented reality is usually not recommended, it could positively impact the user effectiveness or appreciation of the application. For this purpose, we propose an algorithm to compute virtual hand shape in AR, based on inverse kinematics and physical constraints. It allows to naturally grasp virtual objects while keeping the virtual hand on their surface. We compare the influence of this hand representation on performance and user experience in a grasping task in AR, with two control conditions: a simple virtual hand that follows the real hand and a baseline condition without a virtual hand. Results on 48 participants show that all virtual hand conditions decreased user performance, but enhanced the satisfaction with the task.