[Lin]

Question:
Calculate the wavelength, in picometers, associated with an electron traveling 60.0% of the speed of light.

Attempt:
Wavelength = h / (mv)

I know the h value.
The v value I believe it is 60.0% of 3.00 x 10^8
But what is the m value? If the m value isn't given, then the equation can't be solved, can it?
Is there a specific number for the m value?

From the examples I have seem, the m for electrons are always different.

Please help. Thanks in advance.

[Schrödinger]

Use the equation that relates mass of electron (moving with some speed close/comparable to that of light) with its rest mass (9.11 x 10^-31 kg), v and c.

Then substitute value of m de-Broglie's equation.

[Borek]

From the examples I have seem, the m for electrons are always different.

Mass of the non-moving electron (so called invariant mass) is always identical. However, for the moving particle - especially for very high speeds, comparable with c - mass depends for the speed and can be calculated by mutliplying invariant mass by Lorentz factor.