Physics 105 Homework Help Needed

Question

1. A positive charge of 0.00078 C is 28 m from a negative charge of 0.0006 C. What is the force of one of the charges due to the other charge in units of Newtons?
2. Charges Q1 and Q2 exert repulsive forces of 11 N on each other. What is the repulsive force in Newtons when their separation is decreased so that their final separation is 74 % of their initial separation? 
3. What is the potential energy of two charges 1.8 milliCoulombs and 4.3 milliCoulombs separated by a distance of 8 meters? Round your answer to 1 decimal place.  
4. A positive point charge of 0.00042 C is located 3 m from another positive point charge of 3.320889E-5 C. Their electric potential energy is  (Blank 1) J.
5. There is a positive point charge of 0.00036 C. Charge q1exerts a force 6.168 N on a test charge 0.062 C you bought into the electric field of q1. What is the electric field from the charge q1. Their electric field is (Blank 1) N/m.

Answer 1

You should know Coulomb's Law: F_e = k_eQq/d² k_e = 8.99 x 10⁹ Nm²/C²

The formula for electrical potential with respect to a point charge is U_e = k_eQq/d

E field = k_eQ/d² and V = k_eQ/d

That covers 1, 3, 4 by putting in correct values and solving. Note that nC = 10^-9 C

2 is a variation problem F is proportional to 1/d² therefore F₂/F₁ = (d₂/d₁)² not that d₂ = .74d₁

5 qE = F solve for E

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