The figure above represents two charged, concentric conducting shells with radii

Question

The figure above represents two charged, concentric conducting shells with radii R_1 and R_2. The space between the shells is filled with air. The dashed lines represent equipotentials. The electric field just outside the inner shell has magnitude E_1, and the electric field just inside the outer shell has magnitude E_2. Which of the following statements is true of the magnitude E of the electric field at point P? (a) E = 0 (b) E_1 > E > E_2 (c) E = E_1 A ball that can float on water has mass 5.00 kg and volume 2.50 times 10^2 m^3. What is the magnitude of the downward force that must be applied to the ball to hold it motionless and completely submerged in fresh water of density 1.00 times 10^3 kg/m^3? (a) 20.0 N (c) 30.0 N (d) 200 N

Explanation / Answer

6) E = -dV/dt

Potential is constant at point P.

So E = 0

Option a) is correct

7) Totally submerged the ball will displace 25000 cc of water. This will produce an upthrust of 250 N

The ball has a downward gravity force on it of 50 N, so the total force on the ball is 250 up – 50 down = 200 N upward.

An equal but opposite force must be exerted to hold the ball under . 200 N , D) is the answer.

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