The velocity of a particle moving with simple harmonic motion is ______ at the mean position.

79) The acceleration of a particle moving with simple harmonic motion is ______ at the mean position

80) In order to double the period of simple pendulum, the length of the spring should be

81) A pendulum which executes one beat per second is known as

82) When a rigid body is suspended vertically, and it oscillates with small amplitude under the action of the force of gravity, the body is known as