Two stars of masses m and 3m are separated by a distance r and revolve in circular orbits about their common centre of mass under mutual gravitational attraction. The angular velocity of each star is

sqrt(Gm / (4r³))
sqrt(2Gm / r³)
sqrt(4Gm / r³)
sqrt(Gm / (2r³))

Correct answer: sqrt(4Gm / r³)

Solution

For the star of mass m orbiting at radius 3r/4, equating gravitational pull to centripetal force gives omega² = 4Gm/r³, so omega = sqrt(4Gm/r³). Both stars share the same angular velocity.

Related JEE Advanced Physics questions

Rain is falling at an angle α with respect to the vertical at a velocity of 10 m/s. A girl runs in the opposite direction to the rain at a speed of 8 m/s and observes that the rain appears to make an angle β with the vertical. What is the relationship between α and β?
A vector A is turned by a very small angle Δθ radians (where Δθ is much less than 1) to form a new vector B. What is the magnitude of the difference |B − A|?
A swimmer moves through water at a speed of v relative to the water. To cross a river of width d, which flows at a speed u (where u < v), the downstream displacement caused by the river's flow is x. Which of the following is accurate?
A particle is launched from a point with an initial speed u at an angle θ above the horizontal. At a specific point during its motion, its velocity becomes perpendicular to its original direction. What is the time taken to reach this point?
A particle of mass m is projected form the ground with an initial speed u₀ at an angle α with the horizontal. At the highest point of its trajectory, it makes a completely inelastic collision with another identical particle, which was thrown vertically upward from the ground with the same initial speed u₀. The angle that the composite system makes with the horizontal immediately after the collision is
A projectile is launched from level ground with an initial velocity v at an angle θ to the horizontal. The range of the projectile is initially d when the gravitational acceleration is g. If, at the peak of its motion, the projectile enters a zone where the effective gravitational acceleration becomes g' = g/0.81, the new range becomes d'. What is the value of n?

⚔️ Practice JEE Advanced Physics free + battle 1v1 →