Hi, we just started electrostatics in my class, and I amveryconfused about this homework problem.

An infinitely large flat electrode is levitating an objectthatweighs 50 kg. That object has a surface charge of + 75Coulombs.What is the mass density of the electrode?

I know that the electrostatic force will be equal to the forcefromgravity which will be (50kg)*(9.82 m/s). I have no ideawhatformula to use however to determine the mass density.

Thanks a bunch

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Hi, we just started electrostatics in my class, and I amveryconfused about this homework problem.

An infinitely large flat electrode is levitating an objectthatweighs 50 kg. That object has a surface charge of + 75Coulombs.What is the mass density of the electrode?

I know that the electrostatic force will be equal to the forcefromgravity which will be (50kg)*(9.82 m/s²). I have noideawhat formula to use however to determine the massdensity.

Thanks a bunch

Jane, whose mass is 50kg, needs to swing across a river(having width d) filled with man eating crocodiles to save Tarzanfrom danger. However, she must swing into a wind exerting withconstant
horizontal force F on a vine having length L and initially makingan angle ? with the vertical. Taking d=50m, F=110N, L=40m, and?=50degrees.
a) With what minimum speed must Jane begin to swing to just make itto the other side?
b) Once the rescue is complete, Tarzan and Jane must swing backacross the river. With what minimum speed must they begin theirswing? Assume Tarzan has a mass of 80kg.
Answer:

Part a)

D = Lsin + Lsinf, 50=40(sin50+sinf), f = 28.9 degrees

Ki + Ui + Wwind = Kf + Uf

1/2mvi2 + mg(-Lcos) + FD(-1)=0+mg(-Lcosf)

1/2(50)(vi)2 + 50(9.8)(-40cos50)-110(50) =50(9.8)(-40cos28.9)

vi = 6.15 m/s

Part b)

1/2mvi2 + mg(-Lcosf) + FD(+1) = 0+mg(-Lcos)

1/2(130)(vi)2 + 130(9.8)(-40cos28.9)+110(50) =130(9.8)(-40cos50)

vi = 9.87 m/s

I know the answer, but i just need to do it in A B C D method.step a, list the givens and unknowns. step b, write down formulasthat you will use. step c, change up the formula to find theunknowns or the information that you need to figure out. step d,plug in the numbers or in other words the givens to solve theproblem.

I need both parts A and B to be in the A B C Dmethod.

In order to solve the problem you must refer to the first partwhich i already solved and I am 200% sure of the answers, however Iam stuck on the second part and I need help asap. Please do not getscared when you look at this problem and thank you soo much inadvance.

A wheel 75 meters in diameter is mounted vertically on an infinitefrictionless plane at the origin. The infinite frictionless planehas a grid of Cartesian coordinates on it. The moment of inertia ofthe wheel is mr^2. The mass of the wheel is 2000kg. There is anengine connected to the wheel that can produce a torque of 2.34x10^6 Nm. There is a 50 kg object attached to the circumference ofthe wheel that is attached to the wheel with a remote releasemechanism. The wheel is placed on the origin so that the plane ofthe wheel contains the point x=50 meters and y=86.8 m. The wheel ispositioned so that the object is just above the plane at the 6o'clock position. The engine is engaged and begins to apply thetorque to the wheel at 12:00 noon on March 1, 2011. The wheelbegins to rotate in the counterclockwise direction. The torque isapplied for 4 x 10^4 revolutions. At that point the object isreleased from the wheel and a 75 Newton motor accelerates theobject in the direction it is released. The motor is fired for 2.34x 10^4 seconds. (the following questions i have already answered)What is the angular velocity and rotational KE of the object justbefore it is released? (answer for that is 6.39 x 10^2 rad/sec and5.89 x 10^11 J). What angle does the path of the object make withthe x axis? (answer is 60.05 degrees). Where is the object on theinfinite frictionless plane when the motor stops (what are itscoordinates....answer is x=4.85x10^8m y=8.40x10^8m). What is thevelocity and linear KE of the object when the motor stops?(5.91x10^4 m/sec and KE= 8.73 x 10^10J). How much work was done onthe object up until the time the motor stopped? (8.73 x 10^10J).(Hint: the mass of the wheel is 2050 kg while the torque is appliedand the object is attached).

YEA I know what you are thinking at this moment. Difficult right?Please give it a chance and have faith in yourself. Here is thepart I had difficulty with:

After the engine stops firing the object is turned around so thatthe engine can be used to stop the object. The motor is fired atits rated thrust to stop the object. Unfortunately it malfunctionsand shuts down after an hour and the object coasts from then on. Atthe end of an hour of coasting it encounters a ramp that is 2000meters high and slopes up at an angle of 20 degrees. The objectclimbs the ramp and flies off the ramp into the air when it reachesthe end of the ramp. It strikes the plane and digs a crater 5meters deep in the plane and comes to a stop. How far from the endof the ramp does it land? Where does it land on the plane (as incoordinates)? What is the resultant velocity of the object and whatis the acute angle of the resultant velocity with the plane when itstrikes the plane? What is the KE of the object when it hits theplane? What date and time is it when the object lands on the plane?How much work was done on the object to stop it? How long did ittake to stop? What was the deceleration of the object in m/sec^2?What was the force on the object in Newtons to stop it?

If you are from MIT I have faith that you can do this. I am only ajunior in high school taking first year physics that is not evenAP. My teacher is from MIT and said he did this kind of stuff whenhe was there. Please please please help me! I'm desperate.

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