What is the universal law of gravitation?

The two stars in a certain binary star system move in circular orbits. the first star, alpha, has an orbital speed of 36 km/s. the second star, beta, has an orbital speed of 12 km/s. the orbital period is 137 d. a) what is the mass of the star alpha? b) what is the mass of the star beta?

Amoving freight car collides with an identical one that is at rest. if momentum is conserved, what happens to the second car after the collision? it attains the same speed as the first car. it moves at half the speed of the first car. it moves at twice the speed of the first car.

1. do the particles in the medium material move in the same direction of the wave or at opposite direction to the wave? explain your answer. 2. by inputting more energy into the wave, i. e a large shake of the spring, which wave property also increases? 3. are there forces of friction acting while a wave is passing through a medium?