Physic Labs

International Physics Olympiad · Year 2009

Problems

  1. Problem 1A body of mass m moving in a straight line at speed u sticks to a stationary body of mass M on a smooth horizontal surface. The two bodies move together after impact; the collision is brief so external horizontal impulse is negligible. (a) Use momentum conservation to find common velocity v. (b) Calculate kinetic energy before and after impact and the mechanical energy converted to other forms. (c) Express the loss relative to initial kinetic energy and discuss limits M≫m and M→0. Use SI units throughout and treat components as ideal exactly as specified. State sign conventions when writing equations and retain units in final results.Solutions: 1
  2. Problem 2A parallel-plate capacitor of initial capacitance C is charged to V₀ and then completely disconnected from its source and leads. A linear dielectric of relative permittivity κ>1 is inserted to fill the gap; neglect fringing and assume the plates do not move. (a) Find initial charge Q₀, which remains conserved during insertion. (b) Calculate final capacitance and voltage V_f. (c) Compare initial and final field energies and state the work done by an external agent in slow insertion. Use SI units throughout and treat components as ideal exactly as specified. State sign conventions when writing equations and retain units in final results.Solutions: 1
  3. Problem 3Monochromatic light of frequency f illuminates a metal with work function W. In Einstein’s model, each electron absorbs one photon of energy hf; the maximum kinetic energy K_max of emitted electrons is measured, with material losses neglected. (a) Write energy conservation for an emitted electron. (b) Find K_max and threshold frequency f₀, and state the emission condition. (c) Give stopping potential V_s and explain how increasing intensity at fixed above-threshold frequency affects emission. Use SI units throughout and treat components as ideal exactly as specified. State sign conventions when writing equations and retain units in final results.Solutions: 1