Q.A pulse of light of duration $10^{-6}$ s is absorbed completely by a small object initially at rest. If the power of the pulse is $60\times10^{-3}$ W, calculate the final momentum of the object.

Beyond carrying energy, electromagnetic waves also carry linear momentum and angular momentum -- a genuinely surprising fact, since classically only material particles were thought to carry momentum, yet a beam of light striking and being absorbed by an object transfers momentum to it exactly as a stream of particles would. For a completely absorbed pulse of electromagnetic energy $U$, the momentum delivered is $p=U/c$ (where $U$ equals the pulse's power multiplied by its duration, $U=P\,t$, for a pulse of constant power $P$ lasting time $t$); this is a direct consequence of the relation between energy and momentum for radiation, and lets the tiny but measurable "radiation pressure" of a light source be calculated. This momentum-carrying property is not just a theoretical curiosity: the 2018 Nobel Prize in Physics was awarded for the invention of optical tweezers and the production of high-intensity light pulses, both of which exploit exactly this property. An optical tweezer is a tightly focused laser beam whose momentum is used to trap and physically move microscopic particles or molecules -- for example, separating bacteria and viruses from healthy tissue, or isolating cancerous cells from normal ones, purely through the mechanical push of the light's momentum, with significant medical applications. On an astronomical scale, the same effect explains why a comet's tail always points away from the Sun: sunlight's linear momentum physically pushes the comet's loosened dust and gas outward, away fro …