A group of students are camping in the middle of the forest on a very dark night. Their torch batteries went flat hours ago. In the middle of the night they hear a whining sound at 1500Hz from an approaching object. It gets louder........Louder .... LOUDER, and then the pitch suddenly drops to 1200Hz and starts to become gradually quieter. Assuming the speed of sound is 340ms^-1 find the speed of the unidentified noisy object.