Answer:
10.93 rad/s
Explanation:
If we treat the student as a point mass, her moment of inertia at the rim is
So the system moment of inertia when she's at the rim is:
Similarly, we can calculate the system moment of inertia when she's at 0.456 m from the center
We can apply the law of angular momentum conservation to calculate the post angular speed when she's 0.456m from the center:
Answer:
A. K = 0.546 eV
B. cooper and iron will not emit electrons
Explanation:
A. This is a problem about photoelectric effect. Then you have the following equation:
(1)
K: kinetic energy of the ejected electron
Ф: Work function of the metal = 2.48eV
h: Planck constant = 4.136*10^{-15} eV.s
λ: wavelength of light = 410nm - 750nm
c: speed of light = 3*10^8 m/s
As you can see in the equation (1), higher the wavelength, lower the kinetic energy. Then, the maximum kinetic energy is obtained with the lower wavelength (410nm). Thus, you replace the values of all variables :
B. First you calculate the energy of the photon with wavelengths of 410nm and 750nm
You compare the energies E1 and E2 with the work functions of the metals and you can conclude:
sodium = 2.3eV < E1
cesium = 2.1 eV < E1
cooper = 4.7eV > E1 (this metal will not emit electrons)
iron = 4.5eV > E1 (this metal will not emit electrons)