Physics Homework Chapter 15

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1.  A 7.66 nC charge is located 1.87 m from a 4.46 nC point charge.

(a) Find the magnitude of the electrostatic force that one charge exerts on the other.
 ______ N

(b) Is the force attractive or repulsive?





2. A charged particle A exerts a force of 2.55 μN to the right on charged particle B when the particles are 13.0 mm apart. Particle B moves straight away from A to make the distance between them 16.9 mm. What vector force does particle B then exert on A?
_____ μN to the left





3.A small sphere of mass m = 7.60 g and charge q1 = 29.9 nC is attached to the end of a string and hangs vertically as in the figure. A second charge of equal mass and charge q2 = −58.0 nC is located below the first charge a distance d = 2.00 cm below the first charge as in the figure.

(a) Find the tension in the string.
_____N

(b) If the string can withstand a maximum tension of 0.180 N, what is the smallest value d can have before the string breaks?
_____cm

4. A small sphere of charge q1 = 0.808 µC hangs from the end of a spring as in figure (a). When another small sphere of charge q2 = −0.612 µC is held beneath the first sphere as in figure (b), the spring stretches by d = 3.78 cm from its original length and reaches a new equilibrium position with a separation between the charges of r = 5.15 cm. What is the force constant of the spring?
_____N/m

5. Calculate the magnitude and direction of the Coulomb force on each of the three charges shown in the figure below.

6.00 µC charge:
magnitude
_____N direction

1.50 µC charge:
magnitude
_____N direction

−2.00 µC charge:
magnitude
_____N
direction





6. A small object of mass 3.82 g and charge -18.4 µC is suspended motionless above the ground when immersed in a uniform electric field perpendicular to the ground. What are the magnitude and direction of the electric field?

magnitude
_____N/C
direction





7. An electric field of magnitude 5.25  105 N/C points due west at a certain location. Find the magnitude and direction of the force on a −4.20 µC charge at this location.

magnitude    
_____N
direction





8. An electron is accelerated by a constant electric field of magnitude 315 N/C.

(a) Find the acceleration of the electron.
_____m/s^2

(b) Use the equations of motion with constant acceleration to find the electron's speed after 9.50  10-9 s, assuming it starts from rest.
_____m/s





9. A proton accelerates from rest in a uniform electric field of 600 N/C. At some later time, its speed is 1.38  106 m/s.

(a) Find the magnitude of the acceleration of the proton.
_____m/s2

(b) How long does it take the proton to reach this speed?
_____µs

(c) How far has it moved in that interval?
_____m

(d) What is its kinetic energy at the later time?
_____J

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Before beginning on Problem #10, it may be useful to watch a video that explains vector notation
vector notation is the use of the symbols "î and ĵ" to indicate a direction (apart from a magnitude).


10. Three point charges are located on a circular arc as shown in the figure below. (Let r = 3.76 cm. Let to the right be the +x direction and up along the screen be the +y direction.)















(a) What is the total electric field at P, the center of the arc?
             →
 (Vector)E = ______ î  +  _____ ĵ

(b) Find the electric force that would be exerted on a −4.8 nC point charge placed at P.
              →
 (Vector) F = _____ î + _____ ĵ






11. In the figure below, determine the point (other than infinity) at which the total electric field is zero.

_____m to the left of −2.5 × 10−6 C charge

12. A uniform electric field of magnitude E = 410 N/C makes an angle of θ = 66.0° with a plane surface of area A = 4.00 m2 as in the figure below. Find the electric flux through this surface.

_____N · m2/C

NOTE: in video #12, I make a claim that I think the textbook misrepresents the facts. After looking a second time, I feel I may have actually misinterpreted the textbook. The explanation in the textbook is actually correct (if read in the entirety -- and read slowly).


13. An electric field of intensity 4.5 kN/C is applied along the x-axis. Calculate the electric flux through a rectangular plane 0.350 m wide and 0.700 m long if the following conditions are true.

a. The plane is parallel to the y-z plane
_____ N*m²/C

b. The plane is parallel to the x-y plane
_____ N*m²/C

c. The plane contains the y-axis, and its normal makes an angle of 35° with the x-axis
_____ N*m²/C