Need help with Physics?

Posted on 2015-09-26 08:50:00 in Physics by THONY

You are trying to catch butterflies using a net whose rim is about 10.0 cm in radius. As you swing the net, there is a rush of air passing through it. You can describe the flow of air in terms of the momentum density (momentum per unit volume) of the air molecules, and in fact, you can depict the air molecules' flow as a set of "air field" lines. As the air passes through your net, the air field will be approximately uniform, flowing directly into the net's metal hoop (the field lines would be perpendicular to the net's metallic hoop). You know that the mass density of air in typical conditions is close to 1.3 kg/m^3. You guesstimate that the speed of the net through the air as you swung it was about 2.0 m/s. What is the flux of the air field (the momentum density) through your net? That is, how much of air mass is moving through your net per second?

Imagine replacing the flux of air in the previous problem with a uniform electric field of strength 3.0×107 N/C. Assuming that the field is directed directly into the hoop of your net, how much electric flux passes through the net?

In the electromagnetics lab, you charge up a tiny pith ball and stick it on a needle at 4.0 cm above the table top. You then take a square, thin plastic sheet and hold it that one of its edges lies along the table, its center is 4.0 cm away. The sheet has an area of 64.0 cm^2. You measured the charge on the pith ball to be about -22.0 nC. What is the electric flux through the plastic sheet?

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