3) A light balloon lled will helium of densityr . 1 T9 kgi'm3 is tied to a light string of length L = 3.011] m. The string is tied to the ground, forming an \"inverted" simple pendulum. If the balloon is displaced slightlyr from equilibrium1 a) show that the motion is simple harmonic, [6 pts.) b) and determine the period of the motion. (6 ptS.} Take the density of air to he [.29 [cgi'm3 and the mass of the balloon and string is negligible