To practice problem-solving strategy 25.1 power and energy in circuits. a device for heating a cup of water in a car connects to the car's battery, which has an emf e = 10.0 v and an internal resistance rint = 0.08 ω . the heating element that is immersed in the cup of water is a resistive coil with resistance r. david wants to experiment with the device, so he connects an ammeter into the circuit and measures 10.5 a when the device is connected to the car's battery. from this, he calculates the time to boil a cup of water using the device. if the energy required is 100 kj , how long does it take to boil a cup of water?

The second largest public utility in the nation is the sole provider of electricity in 32 counties of southern florida. to meet the monthly demand for electricity in these counties, which is given by the inverse demand function p = 1,200 – 4q, the utility company has set up two electric generating facilities: q1 kilowatts are produced at facility 1, and q2 kilowatts are produced at facility 2 (so q = q1 + q2). the costs of producing electricity at each facility are given by c1(q1) = 8,000 + 6q12 and c2(q2) = 6,000 + 3q22, respectively. determine the profit-maximizing amounts of electricity to produce at the two facilities, the optimal price, and the utility company’s profit