Define work function.

Determine the maximum wavelength of the photons that can cause photoemission.

Calculate the momentum of an electron that has the same de Broglie wavelength as the wavelength of the photons in (b).

${f_{\min }} = \frac{{2.9 \times 1.6 \times {{10}^{ - 19}}}}{{6.63 \times {{10}^{ - 34}}}} = \left( {7.0 \times {{10}^{14}}} \right)\left( {{\text{Hz}}} \right)$;

${\lambda _{\max }} = \left( {\frac{{3.00 \times {{10}^8}}}{{7.0 \times {{10}^{14}}}}} \right) = 4.3 \times {10^{ - 7}}\left( {\text{m}} \right)$;