Windmills fall under which systems?

Two identical small charged spheres are a certain distance apart, and each one initially experiences an electrostatic force of magnitude f due to the other. with time, charge gradually leaks off of both spheres. when each of the spheres has lost half its initial charge, the magnitude of the electrostatic force will be

Abookcase has a mass of 38 kg and the coefficient of friction between it and the floor is 0.82 what is the maximum force of friction between the bookcase and the floor a 372n b 305n c 412n d 449n

Infrared radiation has wavelengths that are shorter than visible light is part of the visible light spectrum has wavelengths that are longer than visible light has the same wavelengths as ultraviolet radiation