You are rearranging the furniture in your living room. In doing so, you push a 30 kg sofa to the left a total distance of 2 m and then you push it back to the right a distance of 1 m. The coefficient of kinetic friction between the sofa and the hardwood floor is 0.2. (a) What is the work done by friction in moving the sofa? (b) Suppose that you had instead simply moved the sofa to its final position by moving it directly 1 m to the left. What is the work done by friction in this case? (c) From the results you obtained in parts (a) and (b), what can you conclude about the nature of the friction force? Is it a conservative force? Explain.
You are rearranging the furniture in your living room. In doing so, you push a 30 kg sofa to the left a total distance of 2 m and then you push it back to the right a distance of 1 m. The coefficient of kinetic friction between the sofa and the hardwood floor is 0.2. (a) What is the work done by friction in moving the sofa? (b) Suppose that you had instead simply moved the sofa to its final position by moving it directly 1 m to the left. What is the work done by friction in this case? (c) From the results you obtained in parts (a) and (b), what can you conclude about the nature of the friction force? Is it a conservative force? Explain.
You are rearranging the furniture in your living room. In doing so, you push a 30 kg sofa to the left a total distance of 2 m and then you push it back to the right a distance of 1 m. The coefficient of kinetic friction between the sofa and the hardwood floor is 0.2. (a) What is the work done by friction in moving the sofa? (b) Suppose that you had instead simply moved the sofa to its final position by moving it directly 1 m to the left. What is the work done by friction in this case? (c) From the results you obtained in parts (a) and (b), what can you conclude about the nature of the friction force? Is it a conservative force? Explain.
•
Nature of Resistance
Temperature-Resistance Relationship
Ohm's Law, Energy and Power
Kirchhoff's Law
• Maxwell's Mesh Analysis
1. A coil of copper wire (p = 10.37 2-cmil/ft) has a length of 600 ft. What is the length of an aluminum conductor
(p 17 cmil/ft), if its cross-sectional area and resistance are the same as those of the copper coil? (Hint: Look
for conversion of inches to mils and square inches to square foot. Include it in your solution.) (1 pt)
2. The copper field winding of an electric machine has a resistance of 46 at temperature of 22°C. What will be
its resistance at 75°C? (Use do = 0.00427 /°C for copper) (1 pt)
3. The resistivity of a copper rod 50 ft long and 0.25 inch in diameter is 1.76 μ at 20°C. What is its resistance at -
20°C? (1 pt)
4. When two resistors A and B are connected in series, the total resistance is 36 2. When connected in parallel, the
total resistance is 8 Q. What is the ratio of the resistance RA to resistance RB? Assume RA < RB. (1 pt)
5. The…
2. Two equally strong individuals, wearing
exactly the same shoes decide to do a tug of
war. The only difference is individual A is
2.5 meters tall and individual B is 1.5 meter
tall. Who is more likely to win the tug of
war?
6. A car drives at steady speed around a perfectly
circular track.
(a) The car's acceleration is zero.
(b) The net force on the car is zero.
(c) Both the acceleration and net force on the car
point outward.
(d) Both the acceleration and net force on the car
point inward.
(e) If there is no friction, the acceleration is
outward.
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