Shares of Tesla Motors opened sharply lower on Friday as a pair of executive departures added to the sense of turmoil surrounding the electric car maker.About six minutes into trading, shares of Tesla had fallen 8.9 percent to $255.94, accelerating the losses from the open.The decline came as chief accounting officer Dave Morton announced his departure after a month on the job, while human resources chief Gabrielle Toledano told Bloomberg she planned to exit the company, not returning from a leave of absence.