What will be the source velocity to make the apparent frequency be equal to the half of the real frequeny?

A body weights 63 N on the surface of the earth. What is the gravitational force on it due to the earth at a height equal to the half the radius of the earth?

A train is moving with a uniform speed of 33 m/s and an observer is approaching the train with the same speed. If the train blows a whistle of frequency 1000 Hz and the velocity of sound is 333 m/s, then the apparent frequency of the sound that the observer hears is