Two spherical bodies of mass M and 5 M and radii R and 2

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Two spherical bodies of mass M and 5 M and radii R and 2 R released in free space with initial separation between their centres equal to 12 R. If they attract each other due to gravitational force only, then the distance covered by the smaller body before collision is

1. 4.5 R
2. 7.5 R
3. 1.5 R
4. 2.5 R

Correct Option: B

Let the distance moved by spherical body of mass M is x₁ and by spherical body of mass 5m is x₂
As their C.M. will remain stationary
So,(M) (x₁) = (5M) (x₂) or, x₁ = 5x₂
x₁ + x₂ = 9R
So, x₁ = 7.5 R