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# A small plastic ball of mass m 5 2.00 g is suspended by a string of length L 5 20.0 cm in a uniform electric field, as shown in Figure P15.52. If the ball is in equilibrium when the string makes a u 5 15.0° angle with the vertical as indicated, what is the net charge on the ball?

## a. 474 $\mathrm{N} / \mathrm{C}$b. $7.59 \times 10^{-17} \mathrm{N}$c. $4.04 \times 10^{-6} \mathrm{m}$

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##### Andy C.

University of Michigan - Ann Arbor

##### Marshall S.

University of Washington

### Video Transcript

had a hello strain slash Tight or discussion. Suppose you have a Hart's office. Okay. And from this heart, so face a ball is hanging. Okay. A small plastic ball is hanging like that. The electric field isn't this direction okay and all. Makes the angle teeter from vertical. Not this ball isn't equilibrium. Okay? Means it's really medium. A group very active rebellion all forces as genome and the mass off the ball is program that is general born Giorgio Dukeegy and the land off the string is 20 centimetre. That is Jill Point to winter. Not a ball is in equilibrium and you have to find out. Nah, charge on this ball. So basically, if electric freely is in this direction, then the fourth also in this direction and due to mass it also experience of force in the downward direction that have forced you to gravity. That is mg now at equilibrium The torque by the force ass Is it close to the talk by the force? I'm cheap. Okay? It means that force into perpendicular distance. If I'm named them a B C force in tow a B in tow. MGI in two b. C so If this is the data, then a B is a closed toe alcohol strata and forced into al coast Aita in tow. AM G in tow. Else I am teeter, uh, simply in triangle ABC course data is a closed toe a B by L. Landau. The string is l So a B is it closed toe Al Costa Similarly, Scientist Isaac was Toby C by l implies that BC's equals two l scientific data. Okay, so by solving these from here, Al will begin Salo and the forces Dewey. So QE course data is a questo. I'm just scientist er from here. Cuban comes out to be and G 10 Peter by e electric field is applied in this direction and the magnitude off electric field is one in tow. Tenderest part three, new turn back Coolum. So, by putting all the values that is curiously questo Oh, we have to find out the queue masses boring geology. Look toe kids into 9.8 meters per second square into 10 50. The angle This is the teeter angle from vertical ist 15 degree is skipping Okay 10 15 degree by one into 10 Respond tree. So by solving this, We will get a value off approximately five point to fight in tow. 10 days by minus six, Coolum. And that will be 5.25 My crook. William, this is the charge on the ball that is in equilibrium. Okay, well, this is all for me for this video. I hope you were like the video.

Other Schools
##### Andy C.

University of Michigan - Ann Arbor

##### Marshall S.

University of Washington