With what velocity must an electron travel so that its momentum is equal to that of a photon of wavelength of `lamda =5000 Å` ?

Explanation

Momentum = mv and `lambda = h//mv`. They are the momentum of an electron and photon respectively. Thus, by equating them would give the velocity.
`:. lambda=h//mv`, Momentum of photon `=mv=h//lambda=(6.626xx10^(-34))/(5000xx10^(-10))"kg m s"^(-1)`
Also, momentum of electron`=mv=9.108xx10^(-31)xx"v kg m s"^(-1)`
Equating, `9.108xx10^(-31)xx v=(6.626xx10^(-34))/(5000 xx 10^(-10)) " or "v= (6.626xx10^(-34))/(9.108xx10^(-31)xx5000xx10^(-10))=1455 ms^(-1)`