MCAT Physics Question 86: Answer and Explanation

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Question: 86

11. A 10 Ω resistor carries a current that varies as a function of time as shown. How much energy has been dissipated by the resistor after 5 s?

  • A. 40 J
  • B. 50 J
  • C. 80 J
  • D. 120 J

Correct Answer: D

Explanation:

Power is energy dissipated per unit time; therefore, the energy dissipated is E = PΔt. In the five-second interval during which the resistor is active, it has a 2 A current for three of those seconds. The power dissipated by a resistor R carrying a current I is P = I2R. Therefore, the energy dissipated is

E = I2RΔt =(2 A)2(10 ?)(3 s)= 4 × 10 × 3 = 120 J

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