The table shows the potential energy and kinetic energy of a skier at two different positions on a hill.

Position and Energy
Position (above ground) Kinetic Energy. Potential Energy
100 meters 0 units. 50,000 units
60 meters 20,000 units. ???
What is the potential energy of the skier at a height of 60 meters above the ground?

30,000 units, because total energy decreases
70,000 units, because total energy decreases
30,000 units, because total energy remains unchanged
70,000 units, because total energy remains unchanged

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.

Work out sian speed for the first 30 minutes of her journey. give your answer in km/h.

The average density of the planet uranus is 1.27 103 kg/m3. the ratio of the mass of neptune to that of uranus is 1.19. the ratio of the radius of neptune to that of uranus is 0.969. find the average density of neptune.