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Question:

Two bodies, each of mass M, are kept fixed at a separation 2L. A particle of mass m is projected from the midpoint of the line joining their centres, perpendicular to the line. The gravitational constant is G. The correct statement(s) is (are)

The minimum initial velocity of the mass m to escape the gravitational field of the two bodies is 4√GML

The minimum initial velocity of the mass m to escape the gravitational field of the two bodies is √2GML

The minimum initial velocity of the mass m to escape the gravitational field of the two bodies is 2√GML.

The energy of the mass m remains constant.

Solution:

Let the two bodies be at (-L, 0) and (L, 0). The gravitational potential energy of the mass m at (0, y) is given by:

U = -GMm/√(L² + y²) - GMm/√(L² + y²)

U = -2GMm/√(L² + y²)

The minimum initial velocity required to escape is given when the total energy is zero. The total energy is the sum of kinetic energy and potential energy:

1/2 mv² - 2GMm/√(L² + y²) = 0

At the midpoint (0, 0), the potential energy is U = -2GMm/L

The minimum velocity required to escape the gravitational field is:

1/2 mv² = 2GMm/L

v² = 4GM/L

v = 2√(GM/L)

Therefore, the minimum initial velocity of mass m to escape the gravitational field of the two bodies is 2√(GM/L).