What is the frequency of a wave having a period equal to 18 seconds? a. 6.6 × 10-2 hertz b. 5.5 × 10-2 hertz c. 3.3 × 10-2 hertz d. 1.8 × 10-2 hertz e. 8.0 × 10-3 hertz

Frequency = 1/period. ... 1 / 18 sec = (1/18) per sec. That's 0.056 per sec or 0.056 Hz. (rounded) (5.6 x 10^-2 Hz)

Answer: a charge of -1.0  × 10⁻⁴ c must be placed  at x = 26 m.the sign of the charge will be the same sign as the  -4.0  µc charge.======electricstatic force between two point charges  is given by    where k is coulomb's constant,  8.99×10⁹  n·m²/c², q₁ and q₂ are the point charges, and r is the distance between the two point charges.assign positive to q₁let q₁ =  6.0 µc, q₂ = -4.0  µc, q₀ represent the charge at the origin, and q₃ represent this new charge to place.the charge at the origin q₀ would experience the following force f₀₁ from q₁, with r = 6.0 m (note that 1  µc = 10⁻⁶ c)    the force from q₂    the force from q₃    the net force on the origin charge, q₀, has to be zero for no electrostatic forcehaving an equation where k and q₀ can be divided out of the equation will allow us to solve for q₃    isolating:     a charge of -1.0  × 10⁻⁴ c must be placed  at x = 26 m.the sign of the charge will be the same as the  -4.0  µc charge