A ball strikes a wall with a velocity →u at an angle θ with the normal to the wall surface and rebounds from it at an angle β with the surface. Then:
If the wall is smooth, coefficient of restitution
Velocity v cos β = u sin θ . . . (i)
vsin β=e.u‘cos θ . . . (ii)
from the above equation, tan β=e cot θ
or tan β=e tan (90∘−θ)
β<(90−θ)
or (β+θ)<90∘
e=tan βtan θ, Hence, (b) is the correct choice