Posts by drwls

Total # Posts: 27,200

  1. physics

    Use the inverse square law. You will need to look up the radius of the earth. It is about 3960 miles, as I recall. Square the ratio of the the distances to the center of the Earth at the top and the bottom of the building. Use that factor to compute the weight at the top, and ...
  2. math

    and she used the money for trip to africa
  3. Math

    Already answered. math - MathMate, Saturday, May 28, 2011 at 11:00pm Here we have 10 digits, of which the first one cannot be zero. If the three digits are distinct, there are 9 choices for the first digit, still 9 (including zero) for the second, and 8 for the third. So 9*9*8...
  4. geometry

    I WON A CAR!!!
  5. geometry

    Where is the road sign? What does Roseville have to d o with it?
  6. Trig

    a. If you are only given the value of ƒÆ , you cannot deduce the value of the radius r. b. ƒÆ = pi - 0.213 rad = 2.929 rad csc ƒÆ = 4.739 c. cos ƒÆ = -0.977 d. cot ƒÆ = 1/(tan ƒÆ )= - (8/(ã3)
  7. Physics

    If T is the half life in days (1.6)/2.0 = (T/156)^(1/2) 0.8 = 0.08006 T^1/2 9.992 = T^1/2 T = 99.8 days The decay constant k is related to the half life by k = ln2/T
  8. Science

    Let the unit cube side be a. Its volume is a^3. Its area is 6a^2. The ratio is a/6. The inscribed sphere has a volume of (pi/6)a^3 and an area of pi*(a/2)^2*4 = pi a^2. The ratio is a/6. The inscribed right cylinder has a volume (pi/4)a^2*a = pi*a^3/4 and an area a*pi*a + 2 pi...
  9. math

    N = 2^1 + 2^2! + 2^(1000!)!) The last number has no ending digits as small as 2 or 4 006 would be the last three digits of the complete number.
  10. physics

    Let the tension be T and the acceleration be a. Write separate free body diagram equations for the two weights T - 100g*sin37 = 100 a 70 g - T = 70 a 170 a = 9.82 g a = 0.058 m/s^2 Now solve for T
  11. Physics Normal force

    Yes. The "normal" force is the perpendicular component. There can be a parallel component as well.
  12. physics

    20 kg wt = 200 Newtons Force Component along ground = 200*cos 60 = 100 N Work = 20 * 100 = 200 J
  13. physics

    For the speed of the car (V), solve V^2/R = 2 m/s^2 V = sqrt400 = 20 m/s The centripetal force is (acceleration)*(Mass) = 2*2500 = 5000 N Centrifugal acceleration is the opposite of centripetal acceleration
  14. iinterpersonal comminication skills

    I agree
  15. geometry

    What is the meaning of P(6,6)? Is it the value of P(x,y) where x = y = 6? Is that 2/(3x) or (2/3)*x on the right?
  16. scince

    The time interval doesn't matter. F = (0.060 kg/s)(15 m/s) = 0.90 N
  17. Physics

    f = (1/2pi)*sqrt(k/M) Hz M = 1481 kg k = 81*9.8/0.015 = 52900 N/m f = 5.0 Hz.
  18. MAT LAB

    unanswered You have used 0 of 4 submissions
  19. General Physics

    The kinetic energy does not change. What does that tell you?
  20. science

    frequency = 600 Hertz (beats per second) Wavelength = (speed of sound)/(frequency) = (340m/s)/600 (s^-1) = 0.57 m
  21. physics

    delta S = entropy change = 1.6*10^5*[1/293 - 1/T2] = 470 Solve for T2
  22. math

    You want to know Young's and the shear modulus, E and G, not Young's and shear modules. The equations you need can be found at Your last sentence is incomplete.
  23. physics

    What are the dimensions of the 2.05? Meters displacement?
  24. earth

    ____ cubic meters, since r is in meters.
  25. physics

    Let ds be the density of steel in kg/liter. Let df be the average density of gasoline. You will need to look it up. Avg density = [2.6 + 15/df]/[2.6/ds + 15]
  26. Physics

    The ratio of the resistances will be the same as the ratio of the resistivities, if lengths and diameters are the same. R(Cu)/R(Al) = 1.72 x 10-8/2.82 x 10-8 = 0.61 R(Al) = 0.509 Ù
  27. heeeeeeeeeeeelp physics vrey tough

    Never mind the General Relativity approach I suggested. Time goes slower at the lower orbit because of Special relativity . Use the two different satellite speeds to deduse the time shift for one orbit. You want the extra credit.. so you do the numbers
  28. help physics very tough

    I assume you are being asked about the change in the rate of a clock in a gravitational field (of the sun, in thic case). There is a General Relativity formula for it. (Due to Schwarzschild, I believe) delta T = T*(delta V)/c*2 V is the gravitational potential at distance d ...
  29. chemistry, not physics

    What does the symbol h represent? The arrow from reactants to products? Here is one answer. 3 H2(g) + N2(g)-> 2 NH3(g) The others are not hard. You need to try them yourself.
  30. Physics

    Plane mass increases by a factor of 2^3 = 8. Plane lift increases by a factor 2^2 = 4 Plane drag increases by an unknown factor between 1 and 2. Engine power will have to increase to compenstate for increased prssure drag and boundary layer friction. The plane's velocity ...

    What questions?
  32. math

    3% gets compounded 20 times. 5000*(1.03)^20 = $9030.56
  33. physics

    Your numbers require units. That is one of the first lessons you ahould have learned about physics.
  34. physics

    How fast is it accelerating? You don't say. To get the power required, you need the kinetic energy at a later time, or the rate of acceleration.
  35. physics

    What kind of length unit is "hm"?
  36. physics

    Don't you mean 90 m/hr? I have never heard of a length unit abbreviated "hm"
  37. Math Linear function help?

    The slope of the line is m = (y2-y1)/(x2-x1) =(3-6)/(4-0) = -3/4 When x = 0, y = 6, so the y-intercept is 6. y = (-3/4)x + 6 is the equation you want.
  38. Physics

    The E-field in any direction is the rate of change of potential with distance along that direction. The a question contains the words"the following", you really must state what the choices are. And please stop changing names.
  39. Physics

    what are the choices?
  40. physics

    Recheck you numbers. Telescopes have long focal lengths and their eyepieces (if used) have short focal lengths. The telescope length, if you are using a refractor, is the sum of the objective and eyepiece focal lengths. Assuming you got the numbers mixed up, the answer is 1.8 m
  41. Physics

    At 60,000 Pa gauge pressure, the absolute pressure inside the ball is 101,325 + 60,000 = 161,325 Pa Dropping the absolute temperature from 293 to 283 K decreases the absolute pressure in the ball by a factor 283/293, resulting in 15,582 Pa. Subtract ambient pressure from that ...
  42. Chemistry

    What you have written in not a balanced chemical reaction. Where is the arrow (->) ? An arrow must separate the two sides of the reaction. What is h2? Cr2O3 is not a gas
  43. Physics

    Write an equation for the E-field along the line joining the two charges. Let the position of the charge be x. Set the E-field equal to zero and solve for x. You can assume that x has to be > 50 cm, so that the fields due to the two charges oppose each other. E = k*[(5.0*10...
  44. physics

    (average velocity)*(time) = 23.9 m/s*12 s = 286.8 m
  45. sam

    Someone left out the word WORK in your question. The question should read: "How much Work do you do if you push a garbage can with a force of 30N while sliding it 4 meters" The answer is Work = Force x Distance, which is 120 Joules in this case.
  46. Sam

    No work is done, because the dock does not move. However, some of the kinetic energy of the wave will be converted to heat and small-scale vorticity and turbulence in the water. A large fraction of the ocean wave energy will also be reflected by the dock.
  47. maths

    For d/dx (3x+2)^n, let u(x) = 3x + 2 f(u(x)^n)= u^n df/dx = (df/du)*(du/dx) = 3*n*u^(n-1) = 3n*(3x+2)^(n-1) For d/dx(2x+3)^m, Let v(x) = 2x +3 g(v(x)^m) = v^m dg/dx = (dg/dv)*(dv/dx) = 2 mv^(m-1) Add the two terms d/dx [(3x+2)^n +(2x+3)^m] = 3n*(3x+2)^(n-1) + 2m*(2x+3)^(m-1)
  48. physics

    Draw a free body diagram and set the total moment about the fulcrum/pivot equal to zero. Let x be the distance of the elder brother from the pivot. 80*x = 50*2 + 30*7 = 310 N*m x = 3.87 m (on the opposite side of the pivot from the 30 N brother) This location is quite near the...
  49. science

    "Plaastids" is misspelled. You will have to write your own poem. This may help:
  50. science

    250 ml of a 1.0 M glucose solution contains 0.25 moles of glucose. Each mole of glucose has a mass of 180 g. 0.25 x 180 = ___ g
  51. MATH

    One row of five posts across from the stream. Two rows of four perpendicular to the stream. Total = 13
  52. language (sentence fluency)

    D. is most fluent
  53. Physics

    The sum of the individual resistances: 15.0 ohms. You do not need the battery voltage for that question.
  54. physics

    Speed is constant and direction is not changing. Therefore acceleration is zero.
  55. Geometry

    You should rethink 4. 2. is 'sometimes'. Consider the isosceles case. 3. is true because of the law of sines
  56. Physics

    (a) +162 F = 90 C (b) 90 K Each 1.8 degree rise in deg F is a 1.0 degree rise in the C or Kelvin Temperature.
  57. math

    ab is not a fraction. It is a product. 56% = 14/25 14 and 25 are coprime numbers a and b. Their sum is a + b.
  58. Physics

    (a) 3 m/s is not an acceleration rate. You probably mean 3 m/s^2. (b) Weight = M*g = 490 N (c) 3 m/s is not a deceleration rate.
  59. Physics

    It is four times the potential due to a charge at a single corner. Your equation 1/4¦Ð = 8.99 ¡Á 10^9 N ¡¤ m2/C2 is obviously incorrect. The distance from the center of the square to a corner is R = 1.414 m The potential due to a single ...
  60. science

    Please be more careful with your spelling. A chemical reaction in which two or more substances undergo a chemical union to form a more complex substance is: a Direct Combination or Synthesis Reaction
  61. algebra

    (a) [f(3) - f(1)]/(3-1) = (28-4)/2 = 12 (b) [f(5) -f(3)]/(5-3) = (76-28)/2 = 24 (c) [f(4) - f(1)]/(4-1) = (your turn)
  62. Physics

    The friction force in the reverse direction is 200*0.4 = 80 N. The net forward force acting on the box is therefore Fnet = 100 - 80 = 20 N Acceleration = Fnet/Mass = Fnet*g/(Weight) = 20*9.8/200 = 0.98 m/s^2
  63. middle madness

    X - 15 - 8 -[(X-15-8)/2) = 46 (X-23)/2) = 46 X -23 = 92 X = 115
  64. math

    Your numbers require dimensions. Inches? Centimeters? Meters?
  65. physics

    The volume of the steel in the coil is V = Length*Width*Thickness = (mass)/(density) = 156 kg/7.9*10^3 kg/m^3 = 1.98*10^-2 m^3 Length = 1.98*10^-2/(0.5)(8*10^-4) = 49.4 meters I have used an "average" density for steel. If you know the alloy type, you can find a more...
  66. Physics

    They have already told you that the velocity of the truck (less sand) remains the same. The momentum of the truck (less sand) therefore also stays the same.
  67. power dissipation

    I = 40V/40,000 ohms = 10^-3 A goes through each resistor, since they are in series. The power dissipated in R1 is I^2*R1 = 10^-6*10,000 = 10^-2 watts
  68. physics

    Convert all speeds to the same units and than compare them. For the bicycle, 18 km/h = 18000 m/3600 s = 5.0 m/s For the car 2 km /min = 2000 m/60 s = 33.3 m/s The athlete runs at 7 m/s. The bike is slowest and the car is fastest in this case.
  69. algebra

    If "diffance" means difference, the answer is 20. You don't need to use algebra.
  70. science

    Don't you mean Fe + 2HCl -> FeCl2 + H2 ? 55g Fe is 0.984 moles 36.5 g HCl is 1.000 moles HCl is slightly in excess of stoichiomentric. 0.984 moles of HCl are evolved. That is 22 liters at STP

    1. Use conservation of momentum. Let the initial direction of X be considered positive. 20 - 12 = -2 + (momentum of Y) Momentum of Y = 10 N*s 2. Momentum of Force*t = 20i + 70j (N*s) is added to the body Initial momentum = 5i -10j Final momentum = 25i + 60 j Divide than by the...
  72. physics

    The magnetic field B provides the centripetal force to keep it in a circular path. e V B = m V^2/R R = mV/(eB) m and e are the electron mass and charge. You don't need the Biot Savart Law for this question. There are plenty of good explanations of it online.
  73. chem ! help its killing me to :/

    This is not a service where long homework assignments are done for you. You have to make an effort. Learn and apply the ideal gas law.
  74. physics

    Use the principle of superposition. The E field at the center will be the sum of two cases: (a) +3 microC at the open corner, and all three other corners (b) -6 microC at the open corner location only Case (a) results in a net E field at the center of zero. That leaves you ...
  75. Physics

    Are you talking about sound waves? You need the speed of wave propagation to answer the question. For sound in air, it is about 340 m/s. Wavelength = (Wave speed)/(Frequency) You do not need to make approximations for pi to do the calculation.
  76. Physics : Young's Modulus

    The effective spring constant of the string is k = Y*S/L Newtons/meter When the mass m is dropped from the fixed end, the string will stretch a maximum amount dL, so that m g L = (1/2) k *dL^2 = (1/2)Y*S/L*dL^2 dL^2 = 2 m g L^2/(Y*S) dL/L = sqrt[2 m g/(Y*S)] If the string is ...
  77. math,science

    cosa = -0.6 a = 126.87 degrees or 233.13 degrees Your requirement that 180<a<360 degrees requires you to pick the second value for a. Now calculate 3tana + 25sin^2a I get 4 + 16 = 20.
  78. PHYSICS FINAL (orbital)

    The satellite's mass doesn't matter. You will need to use the fact that the Earth's radius is 6371 km. The satellite is therefore 9921 km from the Earth's center. The value of the acceleration of gravity (g') there is g' = g*(6371/9921)^2 = 4.046 m/s^2 ...
  79. Physics !!!!! HELP PLEASE

    K.E. is (1/2) M V^2 To get it in Joules, M must be in kg. bullet KE = 960 Joules If motorcycle KE = 960 J,and its mass is 173 kg, (1/2)*173*Vm^2 = 960 then the motorcycle velocity is Vm = 3.33 m/s Convert that to km/h

    See my answer to your same question posted later.
  81. physics

    Average speed = (134+108)/16.8 m/s Average velocity = 26/16.8 m/s
  82. Physics

    Are the batteries and resistors in parallel or series? It makes a difference. There is no "circuit below"
  83. math

    Let x be the number of oranges, y be the number of pears and z be the number of apples. y = 2 z y = x + 4 z = 6 (apples) All you have to do is substitute. y = 12 (pears) x = y-4 = 8 (oranges)
  84. Physics

    Have you read about Coulomb's law? If not, it's time you did. F = k*Q1*Q2/R^2 In your case, Q1 = -Q2 = 2.0*10^-6 Coulombs R = 5.0*10^-2 meters k is the "Coulomb constant", 8.99*10^9 N*m^2*/C^2 Solve for F in Newtons. The force will be attractive since the ...
  85. probability

    This problem is not about geometry You want the probability that Bret's last toss will exceed Shawn's by 11 or more. There are 20x20 = 400 possible outcomes of the two tosses. Here are some of the ways Bret can win ion the last toss. Bret can throw 12 while Shawn ...
  86. Math Please Help

    1/b = 1/50 - 1/a = (a-50)/50a b = 50a/(a-50) If a = 100, b = 5000/50 = 100 If a = 75, b = 150 There are no other integer a values ¡Üb that yield an integer for b. 50/(a-50) would have to be an integer
  87. math i don't get it

    There are two cups of food coloring per 16 gallons of lemonade. Please reread the answers with more care.
  88. math i don't get it

    There is one ounce of food coloring per gallon of lemonade. So... There are 16 ounces in 16 gallons. 16 ounces of food coloring are two cups. You need to use the fluid ounces to cups conversion factor: (8 fl. oz. per cup)
  89. understanding angles

    An angle and an angel are two different things. This would be a good time to learn the difference. If you cut a pie into 72 degree equal slices, you make a total of 360/72 = five pieces. Just how many pieces are left does not affect the answer. They only want to know how many ...
  90. These are my last couple! Please Help In Math.

    Your questions are incomplete and many contain unexplained symbols.
  91. physics

    -g = -9.8 m/s^2 The angle and the speed don't matter. Gravity provides the acceleration
  92. physics

    1050 N/C field strength means the same thing as 1050 Volts per meter voltage gradient between the plates. 1050*d = 30.3 Solve for plate separation d. d = 0.0289 m
  93. Algebra

    For the first part, use conservation of energy, and let Vo be the initial veloicty (Vo^2)/2 = gH Solve for maximum height H H = 240 m Time to reach maximum height = H/V(average) = 240/34.3 = 7.43 s
  94. Physics

    Tangential force = (tangential acceleration) x (mass) = (35/11)m/s^2*1100 = 3500 N Centripetal force at 15 m/s = (V^2/R)*(mass) = 15^2/500 x 1100 = 495 N (It continues to rise as the car accelerates)
  95. Physics

    Four times as much, 496 N, can be lifted. The mechanical advantage tells you that.
  96. physics

    60 mph = 88 ft/s = velocity change Acceleration = 88/10 = 8.8 ft/s^2 That is 0.27 g's.
  97. Science

    Yes. At equivalent distances from the magnets, stronger magnets have stronger B-fields.
  98. German

    ..wir machen Fotos. So many commas would probably not be used.
  99. math

    Divide f(0) - f(-1) by the change in x. You have to know what the function f(x) is.
  100. Physics

    A free body diagram of forces acting on the ball should tell you that Tan 35 = (mg)/(mv^2/R) = R g/ v^2 The mass m cancels out. Solve for v.
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