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Babynini
 one year ago
Force and work.
Babynini
 one year ago
Force and work.

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Babynini
 one year ago
Best ResponseYou've already chosen the best response.0A car drives at 800ft. on a road inclined at 9 degrees. Car weighs 2700lb. Thus gravity acts straight down on the car with a constant force of f=2700j. Find the work done by the car in overcoming gravity.

Babynini
 one year ago
Best ResponseYou've already chosen the best response.0Um..what i've done so far is v=2700cos(9) = 2666.76 which is the force experienced by the driveway. Is that the answer i'm looking for?

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2Work = Force * Displacement

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2Gravity is pulling straight down, so when we think of "displacement" we are only considering the vertical displacement of the car

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2dw:1433399821064:dw

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2when you wrote `Thus gravity acts straight down on the car with a constant force of f=2700j` that doesn't make any sense. Joules aren't a measure of force. They are measure of energy. You might be thinking of newtons?

Babynini
 one year ago
Best ResponseYou've already chosen the best response.0uhh idk that's what my homework says.

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2oh nvm, 2700j is a vector, not 2700 joules

Babynini
 one year ago
Best ResponseYou've already chosen the best response.0where is hte 800 from?

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2"A car drives at 800ft"

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2I'm assuming it drives up that incline and drives 800 ft

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2use trig to find the value of y in the drawing below dw:1433400113262:dw

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2so the car essentially goes up vertically 125.148 ft this is the vertical displacement we care about

Babynini
 one year ago
Best ResponseYou've already chosen the best response.0(ps: it says you are expected to use vectors and the appropriate formulas to find work. Just as a note. :P)

Babynini
 one year ago
Best ResponseYou've already chosen the best response.0so now we have 2=2700 * 125.148

Babynini
 one year ago
Best ResponseYou've already chosen the best response.0that 2 was meant to be a w

Babynini
 one year ago
Best ResponseYou've already chosen the best response.0er. that will make a very nasty negative number..

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2were you given the vector formula for work in physics?

Babynini
 one year ago
Best ResponseYou've already chosen the best response.0give me a moment to find it, I have a formula somewhere :)

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2I'm thinking you basically take the force needed to climb that vertical distance and multiply it with the vertical distance I'm not sure how to fit in vector formulas though

Babynini
 one year ago
Best ResponseYou've already chosen the best response.0so an example given is: A man pulls a wagon horizontally by exerting a force of 20 lb on the handle. If the handle makes an angle of 60 degrees with horizontal, find the work done in moving the wagon 100ft Solution: We choose a coordinate system with the origin at the initial position of the wagon. That is, the wagon moves from point p(0,0) to the point Q(100,0) the vector that represents this displacement is d=100i The force on the handle can be writen in terms of components as F= (20cos(60))i + (20sin(60))j F = 10i+10 sq3j Thus the work done is (10i+10 sq3j)*(100i)=1000 = 1000

Babynini
 one year ago
Best ResponseYou've already chosen the best response.0so our displacement is D = 800i

Babynini
 one year ago
Best ResponseYou've already chosen the best response.0so it's written as F=(2700cos9)i+(2700sin9)j = 2666.785i+422.373j

Babynini
 one year ago
Best ResponseYou've already chosen the best response.0and work done is = (2666.785i+422.373j)*(800i)

Babynini
 one year ago
Best ResponseYou've already chosen the best response.0I'm not sure how they calculated the last part though.

Babynini
 one year ago
Best ResponseYou've already chosen the best response.0Is this kind of making sense? I'm following formulas mostly. o.0

Babynini
 one year ago
Best ResponseYou've already chosen the best response.0(sorry, i'll be patient ;))

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2sorry I got distracted for a sec but it looks like you're on the right track. You dot product the force vector F and the displacement vector d to get the work

Babynini
 one year ago
Best ResponseYou've already chosen the best response.0it's ok! I know you're helping other people. Keep up the hard work :)

Babynini
 one year ago
Best ResponseYou've already chosen the best response.0so is 2133829.189 the final answer you're getting?

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2The force of gravity is F = 0i + (2700j) essentially this vector pulls the car straight down with magnitude 2700 lb  The displacement vector d = 800*cos(9)i + 800*sin(9)*j  dot product the two vectors W = F dot d W = [0i + (2700j)] dot [800*cos(9)i + 800*sin(9)*j] W = [0*800*cos(9)] + [2700*800*sin(9)] W = 337,898.444486899 That seems like a pretty massive number, so I'm not 100% sure

Babynini
 one year ago
Best ResponseYou've already chosen the best response.0bleh yeah that's pretty huge :/

Babynini
 one year ago
Best ResponseYou've already chosen the best response.0wait why 800 instead of 2700 before the cos and sin?

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2because if we ignore the weight, and we just consider moving along the hypotenuse, we basically have this triangle dw:1433402120340:dw

Babynini
 one year ago
Best ResponseYou've already chosen the best response.0but in the example one they used the weight of the cart in that spot of the equation, which is why I ask. hm but yeah I see what you're saying.

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2dw:1433402181444:dw

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2dw:1433402210524:dw

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2hmm now I'm not sure. I've looked back at your example and you're right

Babynini
 one year ago
Best ResponseYou've already chosen the best response.0lol. What is this madness.

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0\[W=\vec F. \vec s=Fs \cos(\theta)\]

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0Everything is given, just convert to standard units and use formula, feet to metres, pounds to kilograms and degrees to radians

anonymous
 one year ago
Best ResponseYou've already chosen the best response.0dw:1433411117463:dw

Babynini
 one year ago
Best ResponseYou've already chosen the best response.0@rational how do I solve this? There's so many formulas that have been given here D:

Babynini
 one year ago
Best ResponseYou've already chosen the best response.0F = 2700j so = <0,2700> Displacement (or shift) = 800 feet. so = <800,0> all correct so far?

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2<800,0> means you go 800 ft to the right and 0 ft up/down

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2<800,0> = 800i + 0j

Babynini
 one year ago
Best ResponseYou've already chosen the best response.0Yep yep. So now according to W = F * D I dot product <0,2700> * <800,0> ?

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2but the object isn't going on a flat level plane its on an inclined plane

Babynini
 one year ago
Best ResponseYou've already chosen the best response.0where is that incorporated?

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2think of the point \(\Large (r, \theta) = (800, 9^{\circ})\) what is the rectangular (x,y) form of this point?

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2dw:1433463727512:dw what are x and y?

Babynini
 one year ago
Best ResponseYou've already chosen the best response.0Opposite and Adjacent? is that what you're asking?

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2Once you find x and y, you will be able to represent the displacement as a vector <x,y>

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2you use trig to find x and y sin(theta) = opp/hyp sin(9) = y/800 y = 800*sin(9) do the same with x (but use cosine instead)

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2dw:1433464222924:dw

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2so the displacement vector is <790.151, 125.149> or 790.151i + 125.149j

Babynini
 one year ago
Best ResponseYou've already chosen the best response.0and Force still is = <0,2700> ?

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2I'm realizing now that's where the mistake is that's the force of gravity, but we want the force of the car if it asked "what is the work done by gravity?" then we would use F = <0,2700>

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2but instead it says "Find the work done by the car in overcoming gravity."

Babynini
 one year ago
Best ResponseYou've already chosen the best response.0aah hrm. so something to do with the weight?

Babynini
 one year ago
Best ResponseYou've already chosen the best response.0Wait, but it says "the gracity acts straight down on the car with a constant force of 2700j." the force pushing against the car would be the same the car is pushing back though. sot hat would be the force the gar is "pushing against gravity"?

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2maybe to overcome the force of 2700j, the car needs to apply 2700 lb somehow?

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2yeah as you just said

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2I'm not sure though

Babynini
 one year ago
Best ResponseYou've already chosen the best response.0But 2700 is what is being pushed against the car. Which is the same amount the car is pushing back against gravity. So that should still be the force.

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2that might be correct

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2I found this page http://cposcience.com/home/Portals/2/Media/post_sale_content/PHY2/Ancillaries/SkillSheets/Unit_4/10.2_WorkDoneagainst.pdf

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2sorry I'm not that great at physics

Babynini
 one year ago
Best ResponseYou've already chosen the best response.0apparently neither am I ;P

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2if you use that link's formula, be careful to make sure things are converted to metric

Babynini
 one year ago
Best ResponseYou've already chosen the best response.0er but this is vector stuff not joules and what not

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2pounds > kilograms feet > meters

jim_thompson5910
 one year ago
Best ResponseYou've already chosen the best response.2joules is just the units of work in physics
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