Plaskett's binary system consists of two stars that revolve in a circular orbit about a center of mass midway between them. this statement implies that the masses of the two stars are equal (see figure below). assume the orbital speed of each star is |v with arrow| = 160 km/s and the orbital period of each is 13.7 days. find the mass m of each star. (for comparison, the mass of our sun is 1.99 1030 kg.)

 M = 4.61 10³¹ kg

Explanation:

For this exercise we will use Newton's Second Law where the force is the gravitational outside

       F = ma

       G M₁ M₂ / r² = m a

The acceleration is centripetal

       a = v² / r’

Let's replace

The mass of the two stars in it, the distance between them is r and the distance around the center of mass is

       r’= r / 2

       G M² / r² = M v² / (r / 2)

       G M / r = 2 v²

The linear velocity module is constant, so we can use the kinematic relationship

       v = d / t

The distance of a circle of radius r ’is

      d = 2π r ’= 2π (r / 2)

      d = π r

We replace

      v = π r / T

Let's write the two equations

      v² = ½ G M / r

      v = π r / T

      r = v T /π

      v² = ½ G M π/ vT

      M = 2 v³ T / π G

Let's reduce the magnitudes to the SI system

     v = 160 Km / s = 1.60 10⁵ m / s

     T = 13.7 days (24 h / 1 day) (3600s / 1 h) = 1.18 10⁶ s

Let's calculate

     M = 2 (1.60 10⁵)³ 1.18 10⁶ / (π 6.67 10⁻¹¹)

     M = 4.61 10³¹ kg

the motion of a pendulum is a classic example of mechanical energy conservation. a pendulum consists of a mass (known as a bob ) attached by a string to a pivot point. as the pendulum moves it sweeps out a circular arc, moving back and forth in a periodic fashion.