Physics 1112 Spring 2009 Homework #8, due second section of week of March 9. Quiz on HW#8 and HW#9 first section of week of March 30. Reading: Text 6.4, 7.4, 7.5, 12.4, 8.1 – 8.3 Not all concepts will be covered in class – you are responsible for all material in the reading and in the homework problems. 1. A certain midsize car has front cross-sectional area 1.8 m2, and air drag coefficient 0.30. The density of air is 1.2 kg/ m3. What is the air drag force (in N) acting on the car when it is moving at 50 mi/h (= 22 m/s)? What power does this drag force dissipate (in kW)? What is the air drag force at 65 mi/h (= 29 m/s)? What power does this force dissipate (in kW)? 2. The potential energy of a pair of hydrogen atoms separated by a large distance x is given by U(x) = -C/x6, where C is a positive constant. What is the force that one atom exerts on the other? Is this force attractive or repulsive? Give your reasoning, e.g. do they gain kinetic energy when allowed to approach each other?
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