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# can someone please help with these physics questions?

1) Your car battery is dead, and your friends are helping you start your car with cheap jumper cables. One cable carries current from their car to your car, and a second cable returns that current to their car. As you try to start your car, a current of 60 A flows through the cables to your car and back, and a voltage drop of 5 V appears across each cable. If you replace the cheap cables with cables having half their electric resistance, what voltage drop will appear across each new cable if the current doesn’t change?

2)A radio-controlled car uses four AA batteries to provide 6 V to its motor. When the car is heading forward at full speed, a current of 1.5 A flows through the motor. How much power is the motor consuming at that time?

3) A pair of alkaline D batteries can provide about 98000 J of electric energy at 3.0 V. If a current of 2 A flows through two D batteries while they’re in the circuit of a flashlight, how long will the batteries be able to provide power to the flashlight?

### 1 Answer

- derframLv 711 months agoFavorite Answer
1. E = I*R. If the resistance is cut in half, and the current remains the same, then the voltage drop will be cut in half. 2.5 volts/run

2. P = E*I = 6 * 1.5 = 9 watts

3. 1 joule = 1 watt-second. The batteries are providing 2 amps at 3 volts or 6 watts of power. Let's finesse the units:

98000 J * (1 watt-sec/J) = 98000 watt-sec

98000 watt-s / 6 watts = 16,333sec or 4.5 hours.

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