Question

a) A sprinter must average 24.0 mi/h to win a 100-m dash in 9.30 s. What is his wavelength at this speed if his mass is 84.5 kg?

b) For potassium metal, the work function W (the minimum energy needed to eject an electron from the metal surface) is 3.68 × 10-19 J. Which is the longest wavelength of the following which could excite photoelectrons?

(550 nm, 500 nm, 450 nm, 400 nm, 350 nm)

Answer 1

The easiest way to do 2 is to calculate the energy of each wavelength listed.

For #2, wavelength = h/mv
Of course you must convert 24.0 mi/h to m/s. The easy way to do that is to type in google "24.9 miles/hour to m/s" without the parentheses and hit the enter key.

Answer 2

550