课程名称︰普通物理学乙 课程性质︰医学系必修 课程教师︰朱士维 开课学院： 开课系所︰ 考试日期（年月日）︰2012/01/11 考试时限（分钟）：180 是否需发放奖励金：是, thanks （如未明确表示，则不予发放） 试题 : General Physics for Department of Medicine 2011 Fall Semester Final Term Duration: 180 minutes (For all questions with selections, be sure to explain the reason) 1. [5] Why the concept of center of mass is very important in Newtonian mechanics? 2. [5] Can the coefficient of friction be larger than 1? If yes, give me an example, If not, tell me why not. 3. [5] A person swings on a swing. When the person sits still, the swing oscillates back and forth at its natural frequency. If, instead, the person stands on the swing in such a way that her center of mass is always directly between her feet and the pivot, the new natural frequency is A. greater B. the same C. smaller. 4. [7] Please write down the relationship between the elastic constant of Hooke's law and Young's modulus. Explan why Young's modulus is more useful for material sciences. 5. [5] The adhesion force of liquid A with glass is larger than the surface tension of liquid A itself. If we place a glass capillary into liquid A, what is the liquid height and contact angle inside the capillary? (图略) (选择题) 6. [13] A pitot tube is used to determine the air-speed of an airplane. It consists of an outer tube with a number of small holes B (four are shown) that allow air into the tube; that tube is connected to one arm of a U-tube. The other arm of the U-tube is connected to hole A at the front end of the device, which points in the direction the plane is headed. At A, the air becomes stgnant so that v_A ＝ 0. At B, however, the speed of the air presumably equals the airspeed v of the plane. (a)[10] Use the Bernoulli's equation to show that v ＝ √(2ρgh/ρ_air), where ρ is the density of the liquid in the U-tube, ρ_air is the density of air, and h is the difference in the liquid levels in the tube. (b)[3] On a high-altitude aircraft, the differential pressure is measured to be 180 Pa. What is the aircraft's speed if the density of the air is 0.031 kg/m^3? →→→→→→→→→→→→→→→→→→→→→ ρ_air ↗ ＿＿＿＿＿＿＿ ＿＿＿＿＿＿＿＿＿＿ v ↗ ╱ ︶ ∣ →→→→→→→→ ╱ B ○ ＿＿_ ∣ →→→→→→→→→ ﹉﹉﹉﹉﹉﹉﹉﹉﹉﹉﹉＿ ∣ ∣ →→→→→→→→ ↗ ＼﹉﹉﹉﹉﹉﹉﹉﹉○﹉ ∣ ∣ ∣ Hole A ╲＿＿＿＿＿＿＿︵＿_∣ ∣_＿＿＿＿ ∣ ↘ ∣ ∣ ∣ ∣ →→→→→→→→→→→∣ ∣→→→→∣ ∣→→→→ ∣ ∣﹉↑﹉﹉ ∣ ∣ ∣ ∣ ∣ ∣h ∣ ∣ ∣ ∣ ∣﹍↓﹍﹍ ◥ ◣ ◢ ◤ ◥ ◣＿◢ ◤ ◥＿＿◤ 7. [5] Human body is composed of 75% water and 25% protein. The specifc heat of water and protein are 1 and 0.4, respectively. What is the specific heat of human body? 8. [5] The diffusion constant of oxygen molecule in water is 2000μm^2/sec. In average, how long does it take for an oxygen molecule to diffuse 10μm in water? (This is the time scale for oxygen exchange in cells.) 9. (a)[5] Explain the principle of a fire piston based on the 1st law of thermodynamics. (b)[5] Explain why do we need energy to survive based on the 2nd law of thermodynamics. 10. [5] With appropriate clothing, human can survive indefinitely even if the environment temperature is below 0 degree Celsius. Nevertheless, a person in regular clothing will last for only a few minutes if he is immersed in water just above freezing point. The reason of much faster heat loss in water is due to A. conduction B. convection C. thermal radiation D. evaporation 11. [5] Two identical pulses, on inverted, travel in opposite directions along a stretched string, and interfere destructively when passing. Which of the following is/are true? A. There is an instant at which the string is completely straight. B. When the two pulses interfere, the energy of the pulses is momentarily zero. C. There is a point on the string that do not move up or down. D. There are several points on the string that do not move up or down. 12. (a)[5] The threshold of hearing corresponds to a sound intensity of 10^-16 W/cm^2. Please calculate the pressure variation for this intensity. (The density of air is 10^-3 g/cm^3 and the speed of sound is 330 m/s.) (b)[5] If the threshold of hearing is defined as 0 dB, the threshold of pain is 120 dB. What is the sound intensity of the threshold of pain? 13. [5] From the properties of axons, please find out the conductivity and capacitance of myelin sheath. 14. [5] You have a manual camera with a focal length of 50 mm. It is "focused" at infinity, but you want to take a picture of an object that is only 0.30 m away. What should you do? A. Increase the distance between the lens and the film by 10 mm. B. Increase the distance between the lens and the film by 50 mm. C. Decrease the distance between the lens and the film by 10 mm. D. Decrease the distance between the lens and the film by 50 mm. 15. (a)[5] The size of a cone cell is about 2μm in diameter. Determine the angular resolution of the eye with a single cone being excited. (b)[5] The angular resolution of the eye is also governed by diffraction theory. With 500 nm light, what size of pupil is required for diffraction to achieve angular resolution in (a)? 16. [5] The resolution of electron microscopy is much higher than optical microscopy. The main reason is: A. Electron is heavier than photon. B. Electron is lighter than photon. C. The wavelength of electron is longer than photon. D. The wavelength of electron is shorter than photon. 17. [5] Which on is the dominant molecule of MRI? A. collagen B. myosin C. hemoglobin D. hydrogen E. nitrogen --

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