The maximum speed of a particle on a string in a simple harmonic transverse wave is calculated using the formula 4A/T, where A is the amplitude and T is the period. This calculation is based on the relationship between velocity, frequency, and wavelength, with frequency being 1/T and wavelength equal to 2A. The maximum particle speed is derived from the equation v(x,t) = (ωA)cos(ωt - kx + φ), reaching its peak when cos(ωt - kx + φ) equals 1. The formula reflects that the particle completes two full cycles in one period, thus doubling the speed to 4A/T. This method can be applied to determine the maximum speed for any particle on a string given its amplitude and period.