Need help with last physics question

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thread starter wierdmonkey4 Sep 09 2009 + PM | QUOTE | PERMALINK | REPORT

A pendulum consisting of a small heavy ball of mass M at the end of a string on length L is released from a horizontal position. When the ball is at point P, the strings forms an angle of 30 degrees with the horizontal line (from previous position). - What are the forces acting on the ball at point P? *i thinks its gravitational pull and tension force* - Determine the speed of the ball at point P - Determine the tension in the string when the ball is at point P *i think it should be something along the lines of -M* This is open ended so i need to show all the work, but i dont understand how i should do this

Sx3 09/09/09 + PM | QUOTE | PERMALINK | REPORT

This is to brutal for me

wierdmonkey4 09/09/09 + PM | QUOTE | PERMALINK | REPORT

i regret taking physics so much. I can provide a pic for the problem, but i didnt think it was necessary

finky 09/09/09 + PM | QUOTE | PERMALINK | REPORT

forces? when i was in science we just said random stf like gravity thrust and stf like that.. i dunno bro luv to help tho but i dont do physics. im a psych kid lol.

SilverStrato 09/09/09 + PM | QUOTE | PERMALINK | REPORT

I'm seeing this next year, sorry bro lol.

RJustice 09/09/09 + PM | QUOTE | PERMALINK | REPORT

1. gravitational pull, tension in the string and the force which brings it back to the centre (forgot the name) 2. s=d/t so speed=(current position-original position)/1 second as it takes 1 second to go to the position at 30 degrees (extreme position for a bob is 30 degrees)

blick 09/09/09 + PM | QUOTE | PERMALINK | REPORT

Gravitational Potential

CorruptPanda Sep 09 2009 + PM | QUOTE | PERMALINK | REPORT

1. The ball at point P has gravitational potential energy and as it starts to swing down, this energy is transferred into kinetic energy and when it reaches the peak height again it's full of gravitational potential. 2. To work this out you will need to understand the law of momentum and energy. Momentum - Momentum before must always be equal to the momentum after. Energy - Energy can not be created or destroyed, it can only be transferred from one form to another (this case its potential -> kinetic -> potential) To work out the velocity we are going to use the formula for potential energy: mgh Where m = mass, g = gravitational constant (9.8m.s^-1), h = height. Formula for kinetic energy: 1/2 mv^2 where m = mass, v = velocity For pendulums we are able to derive a formula by letting: Ek = Ep (energy kinetic = energy potential) We are left with: 1/2 mv^2 = mgh which after simple arithmetic we will end up with: v = (2gh) << squareroot of that ( i dont know how to do that sign ) You can do the working yourself. 3. Here as i understand it they are simple asking for the potential energy that the system carries at point P. To do this simply use the potential energy formula as stated above. Hope this helped.

RJustice 09/09/09 + PM | QUOTE | PERMALINK | REPORT

@above: The second one is actually right, I believe. You gave him the energy the ball possesses in 1 not the forces acting on it. I'm not sure about the 3rd answer you gave though

CorruptPanda Sep 09 2009 + PM | QUOTE | PERMALINK | REPORT

RJustice : @above: The second one is actually right, I believe. You gave him the energy the ball possesses in 1 not the forces acting on it. I'm not sure about the 3rd answer you gave though Oh I thought it was clear enough, I never like throwing answers at people, makes them lazy. For 1, what I meant was since at point P there is height, the pendulum at that current state possesses gravitational potential energy which is simply gravitational force acting on the system. You can also mention the tension of the string, but that isn't a force acting on it. The only force is gravity. I am taking into consideration that you are a High School student where all your workings are done in a closed system.

UnownSilence 09/09/09 + PM | QUOTE | PERMALINK | REPORT

Wow. /rethinks doing physics in year 11

wierdmonkey4 09/09/09 + PM | QUOTE | PERMALINK | REPORT

yea yo, its might be ok if you're just taking Physics or Physics honors, but this is frickin AP Physics, and im only in 10th grade

RJustice 09/09/09 + PM | QUOTE | PERMALINK | REPORT

I'm in 10th too, we don't have pendulums but we have that other stuff. The worst chapters are nuclear physics and caliromotry :/

CorruptPanda 09/09/09 + PM | QUOTE | PERMALINK | REPORT

AP physics is just 2 years ahead, not too shabby really if you understand basic fundamentals and also listen in class. If you have a bad teacher just slit yourself now.

blick 09/09/09 + PM | QUOTE | PERMALINK | REPORT

CorruptPanda : 1. The ball at point P has gravitational potential energy and as it starts to swing down, this energy is transferred into kinetic energy and when it reaches the peak height again it's full of gravitational potential. 2. To work this out you will need to understand the law of momentum and energy. Momentum - Momentum before must always be equal to the momentum after. Energy - Energy can not be created or destroyed, it can only be transferred from one form to another (this case its potential -> kinetic -> potential) To work out the velocity we are going to use the formula for potential energy: mgh Where m = mass, g = gravitational constant (9.8m.s^-1), h = height. Formula for kinetic energy: 1/2 mv^2 where m = mass, v = velocity For pendulums we are able to derive a formula by letting: Ek = Ep (energy kinetic = energy potential) We are left with: 1/2 mv^2 = mgh which after simple arithmetic we will end up with: v = (2gh) << squareroot of that ( i dont know how to do that sign ) You can do the working yourself. 3. Here as i understand it they are simple asking for the potential energy that the system carries at point P. To do this simply use the potential energy formula as stated above. Hope this helped. The 2nd question is right but its in too much detail basically you just have to mention that you are taking Ek=Ep which is Mgh=mv^2/2,(g=10m/s^2 In grade 10.) then you solve for V in the equation and your done.