Balls One
June 17th, 2010
Balls One
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 8 Dz Nike ONE Vapor Speed NIB  US $81.01
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 SPAULDING PIN FLITE GOLF BALLS ONE DOZEN NEW IN PACKAGE US $5.99
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 100 Official Nike Near Mint golf ball Bucket US $31.00
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 PEPSI LIGHT BLUE COLORED GOLF BALL NEW NEVER USED US $4.39
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 Brand New One Dozen Wilson Ultra Logo DPS Golf Balls US $25.00
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A stream of 10^6 one microgram ping pong balls per second are uniformly incident on a circular area of radius?
A stream of 10^6 one microgram ping pong balls per second are uniformly incident on a circular area of radius 5 cm. The balls have a speed of 50 cm/sec. Estimate the pressure exerted on the circular area assuming the balls bounce off with their velocity unchanged.
The velocity has to be changed or they can't bounce off. I think you mean the magnitude of the velocity is unchanged and the direction is changed by 180º.
The momentum change for each is thus 2mV or 2(1e-9)(0.5) kg-m/s or
1e-9 kg-m/s
In one second, there are 1e6 of these, so total momentum change is
1e-3 kgm/s
force = momentum / time = 1e-3/1 = 1e-3 Newton
area of plate is π25 = 78 cm² = 0.0078 m²
pressure = F/A = 1e-3/0.0078 = 0.127 Pa
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