What is the resistance of a lightbulb that uses an average p

What is the resistance of a lightbulb that uses an average power of 40.0 W when connected to a 60.0 - Hz power source having a maximum voltage of 170 V

Solution

Rms Voltage

V_rms=V_max/sqrt[2] =170/sqrt[2]

V_rms = 120.2 Volts

Average Power

P_av = V_rms²/R

R=V_rms²=120.2²/40

R=361.25 ohms