Observers `O_(1) and O_(2) ` are at rest and the wall is moving with velocity V_(w) Cart is moving with constant velocity V_(s) towards wall. The source of sound is in the cart, the original frequency of the wave is f. sound has velocity C w.r.t. ground (medium is stationary) Then match the column -I with column-II
`{:(,"Column-I",,"Column-II"),("(A)","Wavelength received by" O_(1) "directly from cart",,"(P)"((C-V_(w))/(C+V_(w)))((C-V_(s)))/f),("(B)","Wavelength received by" O_(2) "directly from cart",,"(Q)"(C+V_(s))/f),("(C)",underset("after reflection from wall")"Wavelength received by driver of the cart",,"(R)"((C+V_(w))/(C-V_(w)))((C-V_(s)))/f),("(D)",underset("reflection from wall")"Wavelength received by" O_(1) "after",,"(S)"(C-V_(s))/f),(,,,"(T)None of these"):}`

Explanation

When source move towards observer w.r.t. medium, distance between two consecutive wavefronts decreases, there by decreasing time taken in travelling from one wave front to other hence increasing frequency. In case of 'A' source moves towards observer w.r.t medium while in B and C source moves away from the observer. Where as in D source doesn't move w.r.t. medium.