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# Need Help? Post Here!

## Question

Need help on a stubborn problem?  Look for it here!

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I'm having trouble solving electrostatic problems No 2b.

I couldn't understand the answer given.

Hope you can explain it  thanks

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Which part of the problem is giving you trouble?

May I recommend starting by finding the electric field strength at X due to A, and the electric field strength at X due to B.  Add them up to get the total electric field strength at X.  You can then do the same for Y.

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Need help on a stubborn problem?  Look for it here!

what year paper is that? and is it cxc

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Not sure where it's from.  Perhaps AndrewPhysic can help?

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its from a local reference book.I'm Malaysian

btw.thanks sir!

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No problem -- hope that helped a bit!

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Hi sir,How do you find the effective resistance?

Where would you start from?

And here's another capacitor question.

p/s:How to differentiate between a charging capacitor and a discharging capacitor?

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For effective or equivalent resistance, you can find a short tutorial here: http://www.aplusphysics.com/courses/honors/circuits/circuit_analysis.html

For the capacitors, they have to tell you in the problem... some capacitor tutorials here: http://www.aplusphysics.com/courses/ap-c/videos/APC-SSCapacitors/APC-SSCaps.html

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1) A boulder flies through the air at 10.3 m/s with kinetic energy 292J

With this info how do i find

A) The mass of the boulder?

What's the boulder's kinetic energy if its speed doubles?

C) What's the boulder's kinetic energy if its speed is halved?

2) A baseball with mass 0.145kg is pitched at 37.6 m/s. Upon reaching home plate, 16.9m away, its speed is 36.1m/s.

I have no idea how to find...

A) If the decrease is due entirely to drag, find the work done by the drag force.

Find the magnitude of the (assumed constant) drag force

3) How far must you compress a spring with k=668N/m in order to store 496J of energy

Where do I start?

4) The total mechanical energy of an object moving at 31.3m/s is 525J, and its potential energy is 174J

A) What's its mass?

I have no idea where to start and what formula to plug numbers. I can not find any of this in my notes......Help

k

N

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1)  Use the KE equation: KE=0.5*m*v2

http://www.aplusphysics.com/courses/regents/videos/EnergyTypes/EnergyTypes.html

2)  First find the acceleration of the baseball.  With the acceleration, you can find the net force, which will allow you to calculate the work.

http://www.aplusphysics.com/courses/regents/videos/Work/Work.html

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I was wondering if you could help me with this question... A person is running in the halls and someone trips them they slide to a grinding stop in 1.600 seconds. If he slides for 4.300 meters determine

A. the initial velocity

B. the acceleration

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Happy to help.  This is a kinematics equation problem, so the video on kinematic equations would be a good place to get started for some background.  You need to know three quantities to determine the other two.  The quantities are:

vi=?

vf=0

d=4.3m

a=?

t=1.6 s

Now use your kinematic equations to determine the two unknowns!

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