Question

An electron and a baseball move at the same speed. Which has the longer wavelength?

A. the baseball

B. the electron

C. Both have the same wavelength.

Answer 1

If both are moving at the same speed the electron must have the longer wavelength dues to its lower mass. See De Broglie's wavelength equation which states:
\[\large w =\frac{ h}{mv}\]where w = wavelength, h = Plancks constant, m = mass and v=velocity.

http://chemwiki.ucdavis.edu/Physical_Chemistry/Quantum_Mechanics/De_Broglie_Wavelength