Q. Two particles moving under the influence of their mutual gravitational force describe circular orbits about one another with a period T. If they are suddenly stopped in their orbits and allowed to gravitate towards each other, show that they will collide after a time T/5,66.
Q. An x-ray beam with wavelength 0.280 nm is directed at a crystal. As the angle of incidence increases, you observe the first strong interference maximum at an angle 28.0^circ. What is the spacing d between the planes of the crystal?