A spring whose spring constant is 270 lbf/in has an initial force of 100 lbf acting on it. Determine the work, in Btu, required to compress it another 1 in.

When a neutral charge, comes into contact with a positive charge they repel each other nothing happens the neutral charge becomes negative they attract each other

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?

The speed of light in a material is 0.50 c. what is the critical angle of a light ray at the interface between the material and a vacuum?