The weight is 45 N, because the three chains hold the sign, and each contributes 15 N.
Notice that the mass would be the weight/acceleration of gravity, m = 45/9.8 kg. But they ask the weight (force, so Newtons)
I think the correct answer is D: Potential Energy.
Since the two waves have equal amplitudes, if the crest of one wave
meets the trough of the other one, they'll add to produce a level of zero
at that location.
Universe contains billions and billions of stars, galaxies, planets, asteroids, comets and many more different type of bodies. These objects emit radiations of varied frequency. In order to study these different kind of objects, different kind of technology is required. There are different type of missions: some contain probes which land on the surface, some orbit the bodies etc. These are for solar system. Yet some are space observatories having detectors to study light from distant objects. Further, there are different detectors for different wavelengths of electromagnetic spectrum.
