IIT JEE , AIEEE Forum - Mathematics , Analytical Geometry

rik_mad

hi
well this is wat i did

the ball will fall vertically down and hit the plane at (1,1,2)

the line joining this point makes an angle cos(theta) = 1/root(3) with normal

the angle of reflection will be same and the ball will be directed along al ine parallel to xy plane making angle cos(theta) = 1/root(3)
with the normal
moreover the plane makes the same angle with the horizontal
i.e angle cos(theta) = 1/root(3)
now to physics
situation is
a ball moving parallel to ground from a point at the incline of the angle mentioned above....so where will it drop
draw a diagram with this it will be clearer..
using kinematics equation
we get that ball drops by 136 and moves laterally by 68(root2)
back to maths
note that when it wil fall again it will again be parallel to z axis
so the point at which it drops will be of form (a,a,b) (jus' like before)
so root((a-1)^2 + (a-1)^2) = 68(root2)
and b - 1 = 136
so u get
(69,69,138)

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