Physic Labs

Asian Physics Olympiad · Year 2007

Problems

  1. Problem 1A car travels at v=20 m/sv=20\,\mathrm{m/s} around a horizontal curve of radius r=50 mr=50\,\mathrm m. The road is banked at angle θ\theta so that the horizontal component of the normal reaction alone provides the centripetal acceleration; there is no lateral friction. Take g=10 m/s2g=10\,\mathrm{m/s^2}. (a) Find the first requested quantity. (b) Find the second quantity. (c) Determine the final result and check its units. (a) Write v (a) Write vertical force balance. (b) Determine the required bank angle. (c) Evaluate it and check the limit as speed tends to zero.Solutions: 1
  2. Problem 2A straight wire segment of length L=0.40 mL=0.40\,\mathrm m carries steady current I=3.0 AI=3.0\,\mathrm A in a uniform field B=0.50 TB=0.50\,\mathrm T. The field makes angle α=30∘\alpha=30^\circ with the current; end effects are neglected. (a) Determine the magnetic-force magnitude. (b) Evaluate it for these data. (a) Find the first requested quantity. (b) Find the second quantity. (c) Determine the final result and check its units. (a) (a) Express the magnetic force as a cross product. (b) Find its magnitude. (c) Evaluate it and state when the force vanishes.Solutions: 1
  3. Problem 3Monochromatic light of frequency f=8.0×1014 Hzf=8.0\times10^{14}\,\mathrm{Hz} illuminates a metal with work function ϕ=2.0 eV\phi=2.0\,\mathrm{eV}. Use h=4.14×10−15 eV sh=4.14\times10^{-15}\,\mathrm{eV\,s} and elementary charge ee; neglect energy losses after emission. (a) Check whether electrons are emitted. (b) Find their maximum kinetic energy. (c) Determine the stopping-voltage magnitude. (a) Find the first requested quantity. (b) Find the second quantity. (c) Determine the final result and check its units. (a) Check the emission th (a) Check the emission threshold. (b) Find the maximum electron kinetic energy. (c) Find the stopping voltage and the metal’s threshold frequency.Solutions: 1