Physic Labs

Asian Physics Olympiad · Year 2023

Problems

  1. Problem 1A simple pendulum consists of a small bob of mass m=0.50m=0.50 kg on a light inextensible string of length L=1.25L=1.25 m attached to a fixed support. The string is displaced to one side until it makes 60∘60^\circ with the vertical and is released from rest. Neglect resistance and take g=10g=10 m/s2^2. (a) Find the bob's height above the lowest point just before release. (b) Find its speed through the lowest point. (c) Find the string tension there. (d) Find the angle to the vertical where kinetic energy equals potential energy above the lowest point.Solutions: 1
  2. Problem 2A proton of charge q=+1.60×10−19q=+1.60\times10^{-19} C and mass m=1.67×10−27m=1.67\times10^{-27} kg moves in a uniform magnetic field B=0.50B=0.50 T. Its initial velocity has magnitude v=2.0×106v=2.0\times10^6 m/s and is perpendicular to B⃗\vec B; neglect gravity. (a) Find the magnetic-force magnitude and orbit radius. (b) Find the angular frequency, ordinary frequency, and period of the motion. (c) The proton is accelerated until its kinetic energy quadruples in the same field; find the new speed, radius, and period.Solutions: 1
  3. Problem 3Monochromatic light of wavelength λ=400\lambda=400 nm illuminates a metal surface with work function W=2.00W=2.00 eV. Use hc=1240hc=1240 eV nm and electron charge magnitude ee. Assume sufficient intensity and photoelectrons emitted in all directions. (a) Calculate the photon energy and maximum photoelectron kinetic energy. (b) Find the stopping potential needed so no photoelectron reaches the collector. (c) For the same metal, calculate the longest wavelength that still produces photoelectrons. (d) Change the light to λ=300\lambda=300 nm and find the new maximum kinetic energy.Solutions: 1