Asian Physics Olympiad · Year 2006

Problems

Problem 1A block is released from rest on a plane inclined at $\theta=30^\circ$ . The kinetic-friction coefficient is $\mu_k=0.20$ and $g=9.8\,\mathrm{m/s^2}$ . Contact is maintained and friction opposes sliding; take the positive axis down the plane. (a) Find the first requested quantity. (b) Find the second quantity. (c) Determine the final result and check its units. (a) Find the normal reaction. (b) Find the kinetic-friction force. (c) Find the acceleration and determine its direction.Solutions: 1
Problem 2An ideal capacitor of capacitance $C=10\,\mu\mathrm F$ is connected to an ideal source holding voltage $V=12\,\mathrm V$ . After electrostatic equilibrium is reached, energy is stored in the electric field between the plates; neglect fringing. (a) Find the first requested quantity. (b) Find the second quantity. (c) Determine the final result and check its units (a) Find the charge on the capacitor. (b) Find its stored electric-field energy. (c) Evaluate both results in SI units.Solutions: 1
Problem 3A stationary source emits sound at $f=500\,\mathrm{Hz}$ in still air, where sound speed is $c=340\,\mathrm{m/s}$ . An observer moves directly toward the source at constant speed $u=20\,\mathrm{m/s}$ ; there is no wind and the source is not moving. (a) Find the first requested quantity. (b) Find the second quantity. (c) Determine the final result and check its units. (a) Find the sound wavelength (a) Find the sound wavelength in air. (b) Find the frequency heard by the observer. (c) Explain the Doppler sign and check that the result exceeds $f$ .Solutions: 1