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Question
If 1020 oxygen molecules per second strike 4 cm2 of wall at an angle of 30° with the normal when moving at a speed of 2 × 103 ms−1, find the pressure exerted on the wall. (mass of one oxygen atom = 2.67 × 10−26 kg)
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Solution
Mass of O2 atom = 16 × mass of 1 atom
= 16 × 1020 × 2.67 × 10−26
m = 42.72 × 10−6 kg
Momentum of the O2 molecule (P) = mv = 42.72 × 10−6 × 2 × 103
P = 85.44 × 10−3 kg ms−1
Momentum normal to the wall at angle 30°
= 85.44 × 10−3 × cos 30°
= 73.99104 × 10−3 kg ms−1
Pressure = `"F"/"A" = "Change in momentum"/"Area"`
= `(73.99104 xx 10^-3)/((4 xx 10^-2)^2)`
= `(73.99104 xx 10^-3 xx 10^4)/16`
= 4.62444 × 10
P = 46.2 Nm−2
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