To operate an electric lawnmower, you use a 30.0 m long extension cord that you

Question

To operate an electric lawnmower, you use a 30.0 m long extension cord that you plug into a stand ard wall outlet; as such, the current passing through the extension cord is 10.0 A. The extension cord is made out of copper wire that has a diameter of 1.3 mm. a. (5 points) What is the resistance of the entire extension cord? b. (5 points) How much energy is dissipated by the extension cord if it takes you 45 minutes to mow the lawn? (5 points) If PECO charges you $0.12/kW-hr for electricity, how much money did the power dissipated by your extension cord waste? (5 points) If enough of this lost energy went into heating the extension cord, find the resistance of the extension cord at 40°C. Assume that the extension cord had a temperature of 20°C when you calculated its resistance in part 2a. Use 0.00393as the temperature coefficient of copper After your extension cord has heated up, would you waste more or less money than you calcu- lated in part 2c? Explain. c. d.

Explanation / Answer

(A) R = rho L / A

R = (1.68 x 10^-8) (30) / pi(1.3 x 10^-3 / 2)^2

R = 0.38 ohm

(B) P = i^2 R = 38 Watt

Energy = P t = 38 x 45 x 60 = 1.02 x 10^5 J

or = (38 W)(45/60 hr) = 28.5 W h

(C) cost = (28.5 x 10^-3 Kwh)(0.12 / kWh) = 0.0034 dollars

(d) R = (0.38)(1 + 0.00393 x 20) = 0.41

now it will use more power.

Related Questions

Navigate

• Browse (All)
• Browse T
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.