The velocity vv of a particle executing SHM is related with its displacement xx from its equilibrium position as follows
v=omegasqrt(a^2-x^2)......(1),
where a and omega respectively represent the ammplitude and the angular velocity of the imaginary particle moving in the reference circle associated with the SHM.
Its velocity is mximum when x=0, then v_"max"=omegaa
Given v_"max"=100"cm/"s and amplitude a =10cm we get
omega=v_"max"/a=100/10=10"rad/"s
We are to find out displacement x when velocity v=50"cm/"s,Insrting the values in equation (1)
v=omegasqrt(a^2-x^2)......(1)
=>50=10sqrt(10^2-x^2)
=>5^2=10^2-x^2
=>x^2=100-25=75
=>x=sqrt75=pm5sqrt3cm
So the velocity of the particle will be 50"cm/s" at a distance 5sqrt3cm from equilibrium position .pm sign represents both sides.