@Roshni Afrin
The heavier part has no horizontal momentum after collision as it falls vertically down. Let the lighter part have a horizontal velocity v.
M* u cos? = 3M/4 * 0 + M/4 * v
v = 4 u cos?
The time duration t before the lighter mass reaches ground:
H = 0 t + 1/2 g t^2
t^2 = 2 H/g = (2,000/g) Tan? (since H=Rtan? /4)
t = 20 √(5 tan? /g) sec
Horizontal Distance traveled by lighter mass after explosion = v t
vt = 80 u cos? √5tan?/g)
= 80 u √(5sin? cos?/g)
= 40 √(10 u² sin2?/g)
= 40 √[10*4000/g] (since u² sin2?/g=4000m ;given)
=8Km
so total range of lighter part =10Km
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