4.[1pt] Two small spheres with charges -4 C and -9 C are held 9.5 m apart. Find the magnitude of the force between them.

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Allyson Bradford
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1 . [pt] A peson scuffing he feet on a wool ug on a y ay accumulates a net chage of - 4.uC. How many ecess electons oes this peson get? Coect, compute gets:.63e+4. [pt] By how much oes he mass incease? Coect, compute gets:.40e-6 kg 3. [pt] hee chages ae aange on a line as shown above. (o each statement select ue, alse. A If Q is positive, Q is negative an Q3 is negative, then Q MUS feel a net foce to the ight. B If Q is positive, Q is negative an Q3 is positive, then Q MUS feel a net foce to the ight. C If Q is negative, Q is negative an Q3 is positive, then Q MUS feel a net foce to the ight. D If Q is positive, Q is negative an Q3 is positive, then Q MIGH feel a net foce to the ight. Coect, compute gets: 4.[pt] wo small sphees with chages -4 C an -9 C ae hel 9.5 m apat. in the magnitue of the foce between them.

2 Coect, compute gets: N Hint: his is an application of Coulomb's Law. 5.[pt] ou chages Aq,Bq,Cq, an Dq (q = C sit in a plane at the cones of a squae whose sies have length = 63.0 cm, as shown in the iagam below. A chage, q, is place at the oigin at the cente of the squae. DAA: A = 4, B = 6, C = 3, D = 6, = 4. Consie the chage at the cente of the squae. What is the -component of the net foce on this chage? Coect, compute gets:.57-0 N 6.[pt] wo point-like paticles ae place 6.0 cm apat an ae given equal an opposite chage. he fist paticle, of mass. g, has an initial acceleation of 8.85 m/s towas the secon paticle. What is the mass of the secon paticle if its initial acceleation towas the fist is 8.50 m/s? Coect, compute gets:.7+0 g 7. [pt]

3 As shown in the figue above, a ball of mass 0.40 gams an positive chage, q =3.8 micoc, is suspene on a sting of negligible mass in a unifom electic fiel. We obseve that the ball hangs at an angle of theta =5.0 o fom the vetical. What is the magnitue of the electic fiel? Coect, compute gets: 3.36e+0 N/C Hint: Daw a fee boy iagam fo the ball. Since the ball is at est the vecto sum of all the foces, incluing the tension in the sting, must be zeo. 8. [pt] he left figue shows seven chages of equal magnitue. Detemine the iection of the total foce on the chage at the oigin ue to all the othe chages. Into which quaant oes the total foce vecto point? Use the ight iagam to aw the iniviual foces (Choose A, B, C o D. Coect, compute gets: D 9. [pt] wo chages, +q an -q, ae locate in the -y plane at points (0,+/ an (0,-/,

4 espectively. Calculate the magnitue of the electic fiel at point P with the supeposition pinciple. Data: q=38.0 nanocoulombs, =3.80mm an P at =76.0mm. Coect, compute gets: N/C Hint: By the pinciple of linea supeposition, the total electic fiel at position P is the vecto sum of the electic fiel contibution fom chages +Q an -Q. 0.[pt] wo paticles of masses 8.7 kg an 5.8 kg an chages 5.9 C an -7.9 C espectively ae sepaate by a istance 37 cm. in the atio of the magnitues of the lectic to Gavitational foces between them. hat is, what is $_{elec}/_{gav}$? Coect, compute gets:.4+0 Hint: Note that the istance between the paticles oes not affect the atio of the foces. he questions asks fo the atio of the *magnitues*, so the answe must be positive.

5 Woke-Out Answes. Recall that the chage of an electon is -.6-9C o is -.6-3µ ch ag e _ given # electons ch ag e _ electon. Recall that the mass of an electon is 9.-3 kg otal _ mass _ incease # electons *9.0 3 kg 3. If Q is -, Q is -, an Q 3 is +, then Q feels a foce to the ight fom both chages. heefoe, the net foce MUS be to the ight. If Q is +, Q is -, an Q 3 is +, then Q will feel a net foce towas the smalle chage. Without knowing the magnitues of the chage, the net foce MIGH be to the ight o left. 4. o solve this poblem, Coulomb s Law is use: kqq 9 k Be vey caeful with units in this poblem. Keep in min that Coulomb s law will be negative since the foce is attactive. kqq q kqq q o _ ch ag e _ A : kqaq A A 45 o _ ch ag e _ B kqbq B B 45 o _ ch ag e _ C kqc Q c c 45 o _ ch ag e _ D D N D A * 45 * 45 * 45 kqdq 45 * 45 kq ( A B C D B C D * 45

6 6. o solve this poblem, use Newton s thi law: a m a m a m m a 7. he units fo this poblem ae in N/C q q q g g net tan( tan( tan( 0 8. Poblem 8 vaies geatly base on iagam. Remembe that like chages epel an unlike chages attact. hey also a as vectos. 9. o, kq kq kq y y fo kq kq kq y cosθ sinθ

7 Net an otal tot ynet net kq 0 0. o this poblem, just use a atio of the two equations Gmm kqq Gmm g kqq g

Physics Courseware Physics II Electric Field and Force

Physics Courseware Physics II Electric Field and Force Physics Cousewae Physics II lectic iel an oce Coulomb s law, whee k Nm /C test Definition of electic fiel. This is a vecto. test Q lectic fiel fo a point chage. This is a vecto. Poblem.- chage of µc is