13. A child wishes to determine the speed a slingshot imparts to a rock. How can this be done using only a
meter stick, a rock, and the slingshot?

One day, after pulling down your window shade, you notice that sunlight is passing through a pinhole in the shade and making a small patch of light on the far wall. you see that the patch of light seems to be a circular diffraction pattern. it appears that the central maximum is about 1 cm across and you estimate that the distance from the window shade to the wall is about 3 m. what is (a) the average wavelength of sunlight? (b) the diameter of the pinhole?

Could someone me find the answer to this problem.

Anybody wanna ? (picture included? )