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Chapter 1: Q14DQ (page 159)
It is often said that 鈥渇riction always opposes motion.鈥� Give at least one example in which (a) static friction causesmotion, and (b) kinetic friction causesmotion.
(a) Walking in the sidewalk in a horizontal direction.
(b) Driving in a curve of highway.
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Question- Neptunium. In the fall of 2002, scientists at Los Alamos National Laboratory determined that the critical mass of neptunium-237 is about 60 kg. The critical mass of a fissionable material is the minimum amount that must be brought together to start a nuclear chain reaction. Neptunium-237 has a density of 19.5 g/cm3. What would be the radius of a sphere of this material that has a critical mass?
You are lost at night in a large, open field. Your GPS tells you that you are 122.0 cm from your truck, in a direction 58.0掳 east of south. You walk 72.0 m due west along a ditch. How much farther, and in what direction, must you walk to reach your truck?
You normally drive on the freeway between San Diego and Los Angeles at an average speed of 105 km/h (65 mi/h), and the trip takes 1 h and 50 min. On a Friday afternoon, however, heavy traffic slows you down and you drive the same distance at an average speed of only 70 km/h (43 mi/h). How much longer does the trip take?
A Simple Reaction-Time Test.A meter stick is held vertically above your hand, with the lower end between your thumb and first finger. When you see the meter stick released, you grab it with those two fingers. You can calculate your reaction time from the distance the meter stick falls, read directly from the point where your fingers grabbed it. (a) Derive a relationship for your reaction time in terms of this measured distance, d. (b) If the measured distance is 17.6 cm, what is your reaction time?
A rather ordinary middle-aged man is in the hospitalfor a routine checkup. The nurse writes 鈥�200鈥� on the patient鈥檚medical chart but forgets to include the units. Which of these quantities could the 200 plausibly represent? The patient鈥檚 (a) mass in kilograms; (b) height in meters; (c) height in centimeters;(d) height in millimeters; (e) age in months
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