सेकंड लोलक (seconds pendulum) का आवर्तकाल कितना होता है?

In an open organ pipe, v3 and v6 are the 3rd and 6th harmonic frequencies, respectively. If v6 − v3 = 2200 Hz, then the length of the pipe is ______ mm. (Take velocity of sound in air as 330 m/s.)

There is a second's pendulum on the surface of the earth. It is taken to the surface of a planet whose mass and radius are twice that of the earth. The period of oscillation of this second's pendulum on the planet will be: