Final answer:
To find the initial voltage across the 5kΩ resistor, it is acknowledged that if a capacitor is involved and fully charged, the initial voltage will be what the capacitor has charged up to. Without a specific circuit diagram, it is not possible to provide an exact voltage value. The voltage across the resistor depends on the capacitor and circuit configuration.
Step-by-step explanation:
To determine the initial voltage across the 5kΩ resistor, we must understand the behavior of the RC circuit in question when the switch is thrown from position a to position b. Unfortunately, without the circuit diagram or additional details, it is impossible to provide an accurate answer.
However, in general, if the switch has been in position a for a long time, allowing the capacitor to become fully charged, then immediately after the switch is moved to b at t = 0, the initial voltage across the resistor will be the same as the voltage across the fully charged capacitor.
Since no specific values of the voltages or the configuration of the resistors are given, we cannot ascertain the exact voltage. The reason is that, once fully charged, the capacitor acts like an open switch, and the current stops flowing in the circuit.
So, the voltage across the resistor would initially be the same as the voltage the capacitor had charged up to, if the circuit configuration allows for a simple direct connection.