de Broglie's wave equation describes that particles have wave properties. The equation is
λ = h/mv
Where λ is the wave length of the particle (m), h is the Planck's constant (6.62607 x 10⁻³⁴J s), m is the mass of a particle (kg) and v is the velocity (m/s).
λ = ?
h = 6.62607 x 10⁻³⁴ J s
m =200 g = 0.2 kg
v = 20 m/s
By substitution,
λ = 6.62607 x 10⁻³⁴ J s / (0.2 kg x 20 m/s)
λ = 1.66 x 10⁻³⁴ m
Hence, the wavelength of the 200 g ball 1.66 x 10⁻³⁴ m.