Two small spheres A and B each of mass M hang from ceiling on strings of length ℓ. Sphere A is drawn aside so that it is raised to a height h0 as shown in the figure and then released. Sphere A collides and sticks to sphere B and the combined mass swings to a maximum height equal to

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Let velocity of A just before collision be
Velocity of A & B combine is V0/2 after sticking due to momentum conservation
Maximum height (h) = .