MasterPhysics 8 soln

# MasterPhysics 8 soln - PHYS-408 Fall 2008 Mastering Physics...

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PHYS-408 Fall 2008 Mastering Physics Assignment #8 Solutions Problem 26.35 Two 1.0 g spheres are charged equally and placed 2.0 cm apart. When released, they begin to accelerate at 150 m/s 2 . (a) What is the magnitude of the charge on each sphere? From the acceleration, we can find the force r F = m r a F = 0.001 kg ( ) 150 m / s 2 ( ) = 0.150 N This must equal the electrostatic force F = 1 4 πε 0 q 1 q 2 r 2 = 1 4 πε 0 q 2 r 2 q 2 = 4 πε 0 r 2 F = 4 π 8.85 × 10 12 C 2 / Nm 2 ( ) 0.02 m ( ) 2 0.150 N ( ) = 6.67 × 10 15 C 2 q = 6.67 × 10 15 C 2 = 8.17 × 10 8 C = 81.7 nC Problem 26.17 (a) What is the magnitude of the net electric force on charge A in the figure? The charge A is repelled by B with a magnitude F 1 = 1 4 πε 0 q 1 q 2 r 2 = 8.99 × 10 9 Nm 2 / C 2 ( ) 1.0 × 10 9 C 2.0 × 10 9 C 0.02 m ( ) 2 = 4.50 × 10 5 N The charge A is attracted by C with a magnitude F 2 = 1 4 πε 0 q 1 q 2 r 2 = 8.99 × 10 9 Nm 2 / C 2 ( ) 1.0 × 10 9 C 2.0 × 10 9 C 0.03 m ( ) 2 = 2.00 × 10 5 N So, F = F 1 F 2 = 4.50 × 10 5 N 2.00 × 10 5 N = 2.5 × 10 5 N (b) What is the direction of the net electric force on charge A in the figure?

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The force away is greater, so the direction is up.
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