It is possible to blow a dime off a table and into a tumbler. Place the dime abo

Question

It is possible to blow a dime off a table and into a tumbler. Place the dime about 2 cm from the edge of the table. Place the tumbler on the table horizontally with its open edge about 2 cm from the dime, as shown m Figure below If you blow forcefully across the top of the dime, it will rise, be caught in the airstream, and end up in the tumbler. The mass of a dime is m = 2.24 g. and its surface area is A = 2.50 times 10-4 m2. How hard are you blowing when the dime rises and travels into the tumbler? Answer: v = 11.7 m/s

Explanation / Answer

From Bernoullis equation, when the velcoity of the air above the dime is strong enough, it will reduce the pressure above it and lift the weight of the dime

Bernoulli's equation in this instance looks like this

P = .5v2

The Pressure difference = P = F/A = mg/A

Density of air is 1.29 kg/m3

(.00224)(9.8)/(2.5 X 10-4) = .5(1.29)(v2)

v = 11.7 m/s

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