# Question: In a dramatic lecture demonstration a physics professor blows hard

In a dramatic lecture demonstration, a physics professor blows hard across the top of a copper penny that is at rest on a level desk. By doing this at the right speed, he can get the penny to accelerate vertically, into the airstream, and then deflect it into a tray, as shown in Fig. 9.42. Assuming the diameter of a penny is 1.90 cm and its mass is 2.50 g, what is the minimum airspeed needed to lift the penny off the tabletop? Assume the air under the penny remains at rest.

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