Wednesday
March 12, 2014

# Posts by Damon

Total # Posts: 15,228

Math
Oh, ok, you did it fine.

Math
yes but what is the question?

Physics
momentum before = momentum after momentum before = .013 * 330 momentum after = .013 * 270 + 2 v so 2 v = .013 (330 - 270)

physics
the bottom of the board is in tension, the top in compression the second question does not mean anything to me (not stressed maybe?)

Calculus
Often if you do not trust your answer, try numbers for example say x = 3.1 -9.61 / (9.61 - 18.6 + 9) = - 9.61 / .01 = -961 next try x = 3.01 but you get the idea. I think your answer is correct. The result is -9/0 which is undefined or infinite.

physics
elastic

math
+2200

science i really really need help
5 that way you can see if the maggots gather even without the light gradient although I would do 3

Physics
volume flow is the same in the big section as the small. pi Rbig^2 Vbig = pi Rsmall^2 Vsmall so Vsmall = Vbig (15^2/5^2) = 9 Vbig then Bernoulli (1/2)rho Vsmall^2 = (1/2) rho Vbig^2 +rho g h 2 g h = (Vsmall^2 - Vbig^2) 2 (9.81)(3) = 81Vbig^2 - 1 Vbig^2 = 80 Vbig^2 so Vbig^2 = ...

Algebra 1
I will give you the substitution method for b. Then you do a and c B. substitution method 7x -3y = 20 7 x = 3 y + 20 x = (3/7)y + 20/7 then 5x +3y = 16 5[ (3/7)y + 20/7 ] + 3 y = 16 (15/7)y + 100/7 + 21/7 y = 112/7 36 y = 12 y = 1/3 go back and get x

science i really really need help
Hypothesis: “There will be a large difference between the number of maggots in a dark environment and the number in a brightly illuminated one.” I want to rule out other possible reasons for the maggots clustering in one end. First put the light on in the left end. H...

science i really really need help
Therefore light intensity is independent and number of maggots is dependent.

science i really really need help
Which do you think after reading that carefully? Number of maggots DEPENDS ON light intensity.

science i really really need help
The number of maggots, n, is a function of (or "depends on") light intensity, i. n = f(i) i is the independent variable and n is the dependent variable. In other words n depends on i.

r = Revenue c = cost p = profit = r-c u = number of units sold dr/du = marginal revenue dc/du = marginal cost so dp/du = dr/du - dc/du = marginal profit at peak profit, changer in profit for another unit sold is zero so 0 = dr/du-dc/du or dr/du = dc/du

Calculating acceleration science
You are welcome. Yes, I was a teacher many years ago.

American history
My guesses 1. Which of the following is one of the reasons that Native American slavery declined quickly? (4 points) The Spanish and Native American populations mixed. Native Americans did not know how to farm European crops. The Spanish converted many Native Americans to Chri...

American History question
Asking a physicist is probably not the right tack to take.

Calculating acceleration science
acceleration is change in velocity over change in time [40 - (-50)] / .03 = 90/.03 = 3000 m/s^2

physics(URGENT!!!!!)
See above for calculating alpha = d^2T/dt^2 I assume that if you folks are taking 8.01 that you are MIT freshmen. Come on now and read carefully and stop asking the same question over and over from someone who took the course in 1955.

physics(URGENT!!!!!)
alpha is my code for d^2T/dt^2, angular acceleration and dT/dt is omega, angular velocity

physics(URGENT!!!!!)
dx/dt = .075 cos T (dT/dt) is: [ .075 cos T ] {dT/dt) BOTH of those are changing with time form is f(t) = a(t) b(t) so f'(t) = a db/dt + b da/dt so d/dt(dx/dt) = [ .075 cos T ]d^2T/dt^2 +{dT/dt) [- .075 sin T ] (dT/dt) or ax = what is said

physics(URGENT!!!!!)
I am taking moments about the cg. The length of the rod is .15 so half of it is .075 ========================== Harder way --------------------------- Force up from floor = Fz Force down from gravity = m g = .1*9.81 = .981 Newtons so .981 - Fz = .1 az where az is acceleration ...

physics(URGENT!!!!!)
F = m A Fz(.075)sin T -Fx(.075)cos T = 1.88*10^-4 alpha .981 - Fz = .1 az Fx = .1 ax ax = -.075 sin T (dT/dt)^2 + .075 cos T alpha az = -.075 cosT (dT/dt)^2 -.075 sin T alpha

physics(URGENT!!!!!)
alpha is d^2T/dt^2 quoting Mum: ".....Then you can solve. Or if you have a nice equation for omega from part a), take a derivative to get the acceleration. ....."

physics(URGENT!!!!!)
Note, when you use the pivot point at the floor for torques be sure to use (1/3)m L^2 instead of (1/12)m L^2 as I did for the origin at the CG.

physics(URGENT!!!!!)
Look at what Mum posted below my first response: Classical Mechanics Physics - Urgent help please - Mum, Monday, December 9, 2013 at 2:52am I don't want you to cheat so I am giving some hints - not full solution. As for part b - Damon gave you everything in his geometrical...

physics(URGENT!!!!!)
Hey, look there is a limit to the number of times that I am going to respond to the same 8.01 question. If you are taking 8.01 you are capable of reading, at least we could in 1955. Scroll and stop spamming.

PHYSICS URGENT DR BOB
Note moment of inertia about cg rather than about end is (1/12)mL^2

Classical Mechanics - Need Help Please
sorry, .4/3

Classical Mechanics - Need Help Please
F = m dV/dt m dV = F dt so change in momentum = integral of F dt F = 1.2 t^2 integral F dt = 1.2 t^3/3 = 50 at t = 5 yes for part b F = 1.2 t^2 - 10(3)(.2) = 1.2t^2-6 integral F dt = 1.2 t^2/3 - 6 t for part 3 P = F dx/dt F = 1.2 t^2 - 6 at 4 sec F = 13.2 Newtons to get dx/dt ...

PHYSICS IMP PLS
The center of gravity of the fuel/rocket system does not move. There is no net force on the rocket-fuel system. The rocket goes right, the fuel goes left. The momentum of the fuel to the left is equal and opposite to the momentum of the rocket to the right. The rocket pushes f...

Classical Mechanics Physics - Urgent help please
You used moment of inertia about center of the ruler. But in your calcs you assume that it is rotating about its end. Shouldn't you use instead moment of inertia bout the end, when calculating KE of rotation?

Classical Mechanics Physics - Urgent help please
I do not see any parts b and c. You only typed part a. I do not have your text or problem sheet or whatever :) for linear Ke we need (1/2) m v^2 but v = vx i + vy j so magnitude of v is sqrt (vx^2+vy^2)

whoops dumb error
loss of PE = m g (.065) = .1 * 9.81 * (.075-.065) = .00981 Joules then go way down to use that .00981 Joules = 3.76*10^-4 (dT/dt)^2 so dT/dt = 5.1 radians/second

Classical Mechanics Physics - Urgent help please
m = 0.1 Kg L = .15 m moment of inertia of ruler about center = (1/12) m L^2 = 1.88*10^-4 Kg m^2 ------------------------------ Method 1 decrease in potential energy = increase in kinetic energy Height of cg = .075 cos T height of cg at start = .075 meters height of cg at 30 de...

Algebra 2
1 ok 2. b^logb(x) = x x = log.5 y .5^x = .5^log.5(y) = y so y = .5^x 3. x = 2^y - 3 x+3 = 2^y log2 (x+3) = y 4. x = 6 + log y log base e or 10 ??? I will assume 10 x-6 = log y 10^(x-6) = y y = 10^x/10^6

math
It takes him 35 + 4 = 39 minutes to get there and 39 minutes to get back so 78 minutes for a round trip 5 hours = 300 minutes 300 + 12 = 312 minutes traveling 312/78 = 4 round trips

I do not know
Do we have any idea what f(x) is? I suppose in general you can integrate by parts int u dv = u v - int[ v du] here maybe u = f(x) and dv = x dx du = f'(x) dx and v = x^2/2 then we would get (x^2/2)f(x) - int [ (x^2/2) f'(x) dx] but that seems rather pointless.

Tension force in the direction of motion = 125 cos 30 = 108 N Work done by rope tension = Tension force in the direction of motion times distance moved = 108*5 = 541 Joules Since the velocity is constant, the horizontal tension force, 108 N is equal and opposite to the frictio...

physics
F = m a G m M/r^2 = m V^2/r m, the mass of the satellite, is irrelevant, cancels. G M = V^2 r distance around circumference = 2 pi r so t = 2 pi r / V or V = 2 pi r/t so G M = (2 pi)^2 (r^3/t^2) or t^2 = (2 pi)^2 r^3/ (G M) here G = 6.67*10^=11 M = 5.98 *10^24 Kg r = 6.38*10^6...

physics
forget the last few lines there, you do not need it

physics
V = i R + L di/dt i will be of form i = I (1-e^kt) where I is the current after a long time determined only by the battery and the resistance because the inductor has no resistance once steady stage is reached. at t = infinity, i =V/R so I = V/R and at t = 0 , V = L di/dt and ...

math
Anything bigger than 1 that ends in a 0 is divisible by five and ten because ten is two times five anything bigger than 5 that ends in a five is divisible by five so I know that both top and bottom are divisible by 5 (5 * 11) / (5 * 16) or 11/16

PHYSICS PLZ
This is a very, very, ideal problem. Nothing will happen unless the electron strays from its course perfectly down the B lines :) (unstable equilibrium)

math
y = -2 x^4 + 9 x^3 + 2 x^2 - 39 x + 18 make a table of x and y x _____ y -2 _____ 0 oh wow -1 _____ 48 0 ______ 18 +1 ______ -12 so a zero between 0 and 1 well, at least we had a zero at x = -2 so (x+2) is a factor so divide this mess by (x+2) so I have (x+2)(-2x^3+13x^2-24x+9...

math
well, lets assume it is water so 32 oz = 1 qt and dat means day (5 oz/min) (1qt/32 oz)(60 min/hr)(24hr/d) = 5*60*24/32 = 225 quarts/day ( drip, drip, drip .........

math
45 yards(3 ft/yd)(12 in/ft) = 1620 in 1 min = 60 sec so 1620 in/60 sec which is 27 inches/second

PRE-ALGEBRA
275 cents/55 minutes = 5 cents/minute

Science
1 heat 2 thermocouple 3 piezoelectric device 4 thermopile 5 photovoltaic cell 6 electrodes 7 electrolyte

calc
x^2 y + x y^3 = 2 x^2 dy/dx +2 x y +3 x y^2 dy/dx +y^3 = 0 dy/dx (x^2+3xy^2) = -2xy-y^3 at (1,1) dy/dx(1+3) =-2-1 or dy/dx = slope = m = -3/4 so y = -(3/4) x + b , what is b, put in (1,1) 1 = -(3/4)(1) + b b = 1 3/4 = 7/4 so y = -(3/4)x + 7/4 or 4 y = -3 x + 7

World history
Spain was extremely powerful and dominated the seas taking what they chose including from the new American continents, until ......

Math
(x+h)^2-x^2 = x^2 + 2 x h + h^2 - x^2 or in other words 2 x h + h^2 or h (2 x + h) divide that by h 2x+h limit as h ---> 0 is 2 x so f(x) = 2 x as h--->0 4 = 2 x x = 2

spam
repeated postings

scroll down for replies
I answered this several times tonight

PreCal
In other words you either have a typo and you mean 10,000 coins, not 1,000 coins, or I am very confused

100 or 10,000 coins?
Your terms are 1, 2 , 4 , 8 or 1 ,2^1 , 2^2 , 2^4 ...... 2^12 that sum is 2^n = 10,001 or n (.301) = 4 n = 4/.301 = 13

PreCal
that is the sum of a geometric series 1000 = sum from n = 1 to n = n of a + ar + a r^2 + a r^3 where a = 1 and r = 2 the sum of the first n terms is a (1-r^n) /(1-r) so here 1000 = 1 (1-2^n)/(1-2) -1000 = 1 - 2^n 2^n = 1001 n log 2 = log 1001 n = 3/.301 = about 10

TYPO
2a^2 b^3 (4a^2 + 3ab -ab) Nah, no b^5 term results Perhaps you mean 2a^2 b^3 (4a^2 + 3ab^2 -ab) which is 8 a^4 b^3 + 6 a^3 b^5 - 2 a^3 b^4 which is B

Physics
I tried to answer this below but coin was misspelled coin has higher heat transfer, will het your finger up faster.

Phys
I answered this for maphette below: physics - Damon, Sunday, December 1, 2013 at 7:18pm The campfire is hot The air above the fire is hot so its density decreases so it rises air rushes in from all sides to replace it as it rises. Sail much?

yes 5^2 + 12^2 = 13^2 (you should know that by the way) so base b at 12 and height a at 5 c is 15 feet forever so dc/dt = 0 2 a (da/dt) + 2 b (db/dt) = 0 ao 5 da/dt = - 12 (6) da/dt = - 72/5

Physics
F = m a m = 5*10^3 Kg 8750 - 2560 = 5*10^3 a 6.19 = 5 a a = 1.24 m/s^2

physics
sorry, I do not know what a coion is. whichever one has a higher heat transfer coefficient will transfer heat to your hand faster.

physics
The campfire is hot The air above the fire is hot so its density decreases so it rises air rushes in from all sides to replace it as it rises. Sail much?

cool question
by the way

MATHS
t tables and s stools 9 times 8 = 72 items so 72 = t + s now let's look at those 8 items 0 tables + 8 stools = 24 legs 1 table + 7 stools = 4+21 = 25 legs 2 tables + 6 stools = 8+18 = 26 legs 3 tables + 5 stolls = 12+15 = 27 legs 4 tables + 4 stools = 28 5 + 3 = 29 6 + 2 =...

Math
Well, I bet it turns out to be a square but anyway: A = b c where b is breadth and c is length 2 b + 2 c = 800 so b + c = 400 c = (400 - b) so A = b * (400-b) A = 400 b - b^2 b^2 - 400 b + A = 0 where is the vertex of this parabola (I assume you do not do calculus) b^2 - 400 b...

Physical Science
The above is from: GEOLOGIC HISTORY OF OKLAHOMA Compiled by Kenneth S. Johnson, Oklahoma Geological Survey

Physical Science
Due to forces within the Earth, parts of Oklahoma in the geologic past were alternately below or above sea level. Thick layers of sediments accumulated in shallow seas that covered large areas. The sediments were later buried and lithified (hard - ened to rock) into marine sha...

PreCal
8 sqrt x = x+16 64 x = x^2 + 32 x + 256 x^2 -32 x + 256 = 0 (x- 16)^2 = 0 x = 16 is the only root I see

Math
6^2 + h^2 = 10^2 36 + h^2 = 100 h^2 = 64 h = 8 or you can see that this is a 3 - 4 - 5 right triangle

PHYSICS
Now your elevator problem and your rope problem are very much the same so look them over carefully.

PHYSICS
Force up on boy = rope tension T Force down on boy = m g acceleration of boy downward = a then ma = mg - T here m = 500/9.81 = 50.97 kg so 50.97 a = 500 - 350 = 150 a = 150/50.97 = 2.94 m/s^2 d = (1/2) a t^2 30 = 1.47 t^2 t = 4.52 seconds assuming 30 meters is the ground then ...

PHYSICS
mass = mg/g = 4900/9.81 = 500 Kg a = acceleration down m a = 4900 -3800 so 500 a = 1100 a = 2.2 m/s^2 DOWN

arithmetic !
2 pi f = 10^6/42 = 2.38*10^4 f = .379 * 10^4 = 3790 Hz

College Physics
reactance magnitude = V/i for inductance V = L di/dt if i = a sin wt di/dt = a w cos wt and V = L a w cos wt magnitude of V/i = Lw = 2 pif L here L = 42 * 10^-6 so reactance = 2 pi f (42*10^-6) for capacitor C = q/V V = q/C = (1/C) integral i dt if i = a sin w t V = (1/C) (a/w...

Chemistry
the second one is very similar except you need to know how many moles of Calcium are 2.94 grams atomic mass of calcium = 40 grams/mole approx so 2.94 g /40 g/mole = .0735 moles of Ca so you will need twice that many moles of HCl

Chemistry
We need 2 moles of HCl for every mole of calcium hydroxide we have 46.5 *10^-3 * .125 = 5.81 *10^-3 moles of calcium hydroxide so we need 11.6 *10^-3 moles of HCl .175 moles/liter * x liters = 11.6*10^-3 moles x = 66.4 * 10^-3 liters = 66.4 mL

PreCal - repost
Note that as time becomes large, N becomes 200/4 or 50 so no matter how long you train, you will never test more than 50 a day.

PreCal - repost
so N = 200 /( 4 +21*.8187) = 9.44

PreCal - repost
e^-.2 = 1/e^.2 = 1/1.2214= .8187

PreCal - repost
N = 200 / ( 4 + 21 e^-.1t) I think may be what you mean

PreCal
You need a calculator or a table e^.2 = 1.2214

PreCal
Terri, Let me start at the top. 1000 at .08 A = 1000 e^ .08 t if continuous compounding double is 2000 so 2000 = 1000 e^.08 t or 2 = e^.08 t now take the natural log of both sides ln 2 = ln [e^.08t) or ln 2 = .08 t because ln (e^anything) = anything now if only we knew ln 2 , ...

PreCal
2 = e^(.08n) ln 2 .08 n but ln 2 = .6931471806

Algebra 1 (Reiny or Kuai)
Include x = 0 for sure :)

Physics Classical Mechanics
mass = rho pi r^2 L weight = m g = rho pi r^2 L g tensile stress at top = weight/pi r^2 = rho L g so for iron 350 * 10^6 = 7.8*10^3 * L * 9.81 so L = 4.57* 10^3 = 4,570 meters long and for titanium 450 * 10^6 = 4.5*10^3 * L * 9.81 so L = 10.2*10^3 = 10,200 meters long

History
I would say A. That is something from which all of us are still benefiting (or in some cases suffering). B is not even legislative action

Math
If the answer is 25, that is not the answer to the question asked which is how many do NOT fit in the box.

Math
5*5 = 25 fit in the box 32 - 25 = 7 She will have to quickly eat seven of them so no one notices that the box is too small.

I did this
Scroll down.

Math
4 is wrong 24 - 15 = 9 more crocodile eggs

Physics
tension in vertical string below table = T1 m1 a = m1 g - T1 so T1 = m1 (g-a) tension in horizontal string above table = T2 m2 a = T2 - m2 g mu so T2 = m2 (a + mu g) then ( T2 - T1 )R = I alpha but alpha R = a so (T2 - T1)R = I a/R or T1-T2 = I a /R^2 T1 -m2(a + mu g) = I a /R...

Physics
20 * 9.81 = force in Newtons work = force * distance = 20*9.81*2 Joules

ALGEBRA
(1/3) + 1 + 3 + 9

math
1.03^10 = 1.344 34.4 percent higher costs in 2002 dollars

without I mean
NEVER do one of these problems without sketching a quick graph off to the side.

MATH
slope, call it m, is m = (Y2-Y1)/(X2-X1) m = (-4 - 4) / (0 - -4) = -8/4 = -2 NOW SKETCH A GRAPH AND LOOK AT THOSE POINTS AND A LINE FROM THE FIRST TO THE SECOND. NEVER do one of these problems with sketching a quick graph off to the side.

physics
say one is along x axis, second is 45 deg toward y axis (East and Northeast), third is 45 degrees down toward - y axis (Southeast) x forces: 1450 + 1450 cos 45 + 1450 cos(-45) = 1450 (1 + .707 + .707) = 1450(2.414) = 3501 Lb y forces 0 + 1450 sin 45 + 1450 sin (-45) = 0 so 145...

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