The mass m bullet penetrates the m object suspended in the rope length L with V0, and the velocity V is used to calculate the tension of the rope

The mass m bullet penetrates the m object suspended in the rope length L with V0, and the velocity V is used to calculate the tension of the rope

Law of conservation of momentum: m * V0 = m * V + m * V '
So V '= m (V0-V) / M
Centripetal force (f-mg) provides centripetal force: f-mg = m * V '^ 2 / L
So f = Mg + m * V '^ 2 / L = Mg + m ^ 2 * (V0-V) ^ 2 / (m * l)