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# A container contains an ideal gas. The wall is hit by "n" molecules / second, each of mass "m" and moving the same velocity "u". The force exerted by the molecules on the wall is?

(A) 0 (B) 1 $mnu$ (C) 0.5 $mnu$ (D) 2 $mnu$

Total mass of molecules striking per second = $mn$.
Momentum with which the molecules strike = $mnu$
Momentum after striking = $-mnu$
Momentum change per second = $mnu - (-mnu) = 2 mnu$
edited Aug 9, 2014