Chemistry
posted by Garcia .
To resolve an object in an electron microscope, the wavelength of the electrons must be close to the diameter of the object. What kinetic energy must the electrons have in order to resolve a protein molecule that is 5.40 nm in diameter? Take the mass of an electron to be 9.11× 10–31 kg.

I am having difficulty determining what would be the wavelength that I use to determine the velocity using de Broglie's equation.

I think you want to use
E = hc/wavelength and solve for E. Then KE = 1/2 m*v^2 and solve for v. 
But what is the wavelenght? Do I use 5.40 nm?