A stream of particles each of mass `m` moving with velocity `v` with number of particles per unit volume `n` strike against a wall at an angle `theta` to the normal elastically. Find the pressure exerted by the exerted by the stream on the wall.

Answer

`2mvnv^(2)cos^(2)theta`

Explanation

Those partcles whose distance from the wall is less than `v` dt will striking the wall in time dt. Assuming the wall area to be `A`, volume of the part will be `A` (vdt) `costheta`
`therefore` No. of molecules `(dn)=n(dv)=n("Av dt") costheta`
change in momentum of each particle `dp_(1)=2mvcostheta`
`thereforeF=(dp)/(dt)=((dn)(dp_(1)))/(dt)=([n("A vdt"costheta)]2mvcostheta)/(dt)=2"A n mv"^(2)cos^(2)theta`
`rArr`pressure`=(F)/(A)=2mnv^(2)cos^(2)theta`