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Question: 10,000 small balls, each weighing 1 gm, strike one square cm of area per second with a velocity 100 ...

10,000 small balls, each weighing 1 gm, strike one square cm of area per second with a velocity 100 m/s in a normal direction and rebound with the same velocity. The value of pressure on the surface will be

A

2×103N/m22 \times 10^{3}N/m^{2}

B

2×105N/m22 \times 10^{5}N/m^{2}

C

107N/m210^{7}N/m^{2}

D

2×107N/m22 \times 10^{7}N/m^{2}

Answer

2×107N/m22 \times 10^{7}N/m^{2}

Explanation

Solution

P=FA=n[mv−(−mv)]A=2mnvAP = \frac{F}{A} = \frac{n\lbrack mv - ( - mv)\rbrack}{A} = \frac{2mnv}{A}

=2×10−3×104×10210−4=2×107N/m2= \frac{2 \times 10^{- 3} \times 10^{4} \times 10^{2}}{10^{- 4}} = 2 \times 10^{7}N/m^{2}