The boy threw a stone into the well. If the depth of the well is 15 meters, determine the time that elapses from the moment the stone is dropped, to the time the boy hears the sound of the stone in the water. The speed of sound in the air is 340 m/s.

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?

What are atoms of the same element with varying number of neutrons

During which interval are the persons represented by the graph not moving? a) 0 to 0.5 hrs b) 1.5 to 2 hrs c) 2 to 2.5 hrs d) 4.5 to 5 hrs