In the figure shown, a spring mass system is placed on a horizontal smooth surface in between two vertical rigid walls W1 and W2. One end of spring is fixed with W1 and other end is attached with mass m which is free to move. Initially, spring is tension free and having natural length l0. Mass m is compressed through a distance a and released. Taking the collision between wall W2 and mass m as elastic and K as spring constant , the average force by mass m on wall W2 in one oscillation of block is
(a) 2aK/pi
(b) 2ma/pi
(c) aK/pi
(d) 2aK/m
