1. People working on the roofs of buildings often lay a plank of wood on the roof. They walk on the plank rather than the roof itself. a) Explain why using a plank will help to prevent damage to the roof.
b) A workman's weight is 850 N, and each of his boots has an area of 210 cm2. Calculate the maximum pressure under his feet when he is walking. Give your answer in pascals. c) The workman lays a plank on the roof. The plank has an area of 0.3 m2 and a weight of 70 N. What is the maximum pressure under the plank when he is walking on it?(1+2+2)

What is the frequency of a light wave with a wavelength of 620nm

Suppose that an electromagnetic wave which is linearly polarized along the x−axis is propagating in vacuum along the z−axis. the wave is incident on a conductor which is placed at z > 0 region of the space. the conductor has conductivity σ, magnetic permeability µ and electric permittivity ε. (a) find the characteristic time for the free charge density which dissipates at the conductor. (b) write the maxwell equations and derive the wave equation for a plane wave propagating in a conductor. (c) find the attenuation distance at which the incident amplitude reduces to e ^−1 of its initial value. (d) find the electric and magnetic fields inside the conductor. 8 (e) find the power loss per area of the incident electromagnetic wave at the surface of conductor.

Aboat radioed a distress call to a coast guard station. at the time of the call, a vector a from the station to the boat had a magnitude of 45.0 km and was directed 15.0° east of north. a vector from the station to the point where the boat was later found is = 30.0 km, 15.0° north of east. what are the components of the vector from the point where the distress call was made to point where the boat was found? in other words, what are the components of vector c = b - a?