A unifrom magnetic field `B` is acting from south to north and is of magntitdue `1.5 Wb//m^(2)`. If a proton having mass `= 1.7xx10^(-27) kg` and charge `= 1.6xx10^(-19) C` moves in this field vertically downwards with energy `5 MeV`, then the force acting on it will be

Options

A. `7.4xx10^(12) N`
B. `7.4xx10^(-12) N`
C. `7.4xx10^(19) N`
D. `7.4xx10^(-19) N`

Answer

B

Explanation

`F = qvB` and `K = (1)/(2) mv^(2) implies F = qB sqrt((2k)/(m))`
`= 1.6xx10^(-19) xx 1.5 sqrt((2xx5xx10^(6)xx1.6xx10^(-19))/(1.7xx10^(-27)))`
`= 7.344xx10^(-12) N`