In first collision mu momentum will be imparted to system, in second collision when momentum of (M+m) is in opposite direction mu momentum of particle will make its momentum zero. On 13th collision, [m]→[M+12]; [M + 13m]→V mu=(M+13m)v⇒v=
mu
M+13m
=
u
15
v=ωA⇒
u
15
=√
K
M−13m
×A Putting value of M,m,u and K we get amplitude A=