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  1. C

    Young Modulus

    I’m fine with part a, answer 3.3 x10^6 but I’m getting 0.00045 for part b when it should be 2.8x10^-4, what am I missing? e = (1500x18)/(1.3x10^11 x 0.000452389)
  2. C

    Mass of ruler moments

    The answer is 127.04g. I’m getting close but can’t get the answer. Using 9.81 for gravity, the force where the balance is is 2.10(58146)N As it is balanced 2.10N x 0.29m = W x 0.50m where 0.50 is the centre of mass That gives W = 1.22N = 124.5g?
  3. C

    Acceleration in terminal velocity?

    I've just read somewhere that acceleration is zero when an object is at terminal velocity? I think it's wrong but wanted to check if I'm right? Yes the resultant force is zero but gravity doesn't disappear so presumably acceleration due to gravity is constant? Terminal velocity means constant...
  4. C

    Current algebra

    Homework Statement An electric circuit consists of 3 identical resistors of resistance R connected to a cell of emf E and negligible internal resistance. What is the magnitude of the current in the cell? (in the diagram two of the resistors are in parallel with each other then the other in...
  5. C

    Electromagnetic Induction and a coil of wire

    The magnetic field that is oriented perpendicularly through a 9.2 cm diameter coil of wire drops from 6.4 T to 6.1 T in 0.076 seconds. What is the emf induced in the coil? Trying to answer this. My question is, if they are perpendicular then does that mean that cos90 makes phi = BAcos theta...
  6. C

    Doppler effect speed of sound

    Homework Statement Problem: a car is moving away from a stationary observer at 25ms^-1. It emits a frequency of 810Hz and the observer hears an apparent frequency of 762Hz. What is the speed of sound in air at that time? Homework Equations The equation for a source moving away is f' =...
  7. C

    Determine its speed immediately before landing

    Homework Statement Please could someone check if I have got this right? Many thanks The question: An object of mass of 1000kg leaves a 64m high cliff at 100 ms-1 before descending to the ground. Ignoring air resistance, determine its speed immediately before landing. Homework...
  8. C

    Current in the cell

    Trying to work out how to do this. I know the answer is B but don't know how. Internal resistance is negligible so I assume I just use I =V/R. I've tried using sample values for R eg 5 and V =10V giving I as 1.3 but am no closer to 2/3. What am I missing?
  9. C

    Attenuation and power loss

    I'm revising attenuation and power loss logarithmic equations. The exam formula I'm given is attenuation = 10 log (I1/I2) I'm trying to confirm what each I stands for. Some of the examples I'm looking at seen to give input/output power, some seem to reverse it. Which is right? What do they...
  10. C

    On a cliff edge!

    Lucy stands on the edge of a vertical cliff and throws a stone vertically upwards. The stone leaves her hand with speed 15m/s at the instant her hand is 80m above the surface of the sea. Air resistance is negligible and the acceleration of free fall is 10m/s/s. First part is to calculate the...
  11. C

    Percentage Uncertainty

    Two lengths, a and b, are measured to be 51+/-1cm and 49+/-1cm respectively. In which of the following is the percentage uncertainty the largest? A a+b B a-b C a x b D a/b The answer should be b but I can't figure out why. I know that for / and x you add the percentage errors so if the error...
  12. C

    Zero electric field strength

    Two isolated point charges -7μC and +2μC are at a fixed distance apart. At which point is is it possible for the electric field strength to be zero? I don't know where to start with only 2 numbers and no distances. I know that E= kQ/r^2
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    Mass of the moon

    I'm looking at a textbook problem which has an answer but no working out. I've read the chapter several times and looked at the equations but can't see where to start with it? Can you help? Assuming the Earth and Moon to be isolated from all other masses, use the following data to estimate the...
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    Gravitational field strength between masses

    Homework Statement A mass at a point X gives rise to a gravitational field strength g at point P as shown. An identical mass is placed at point Y x ________ p ______________________ y The resultant g f s is now? Homework Equations g = Gm/r2 The Attempt at a Solution...
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    Resistivity in a cylinder

    Homework Statement A cylindrical conductor of length l, diameter D and resistivity ρ has resistance R. A different cylindrical conductor of resistivity 2ρ, length 2l and diameter 2D has a resistance A. 2R. B. R. C. R/2. D. R/4 Homework Equations I assume its R = pL/A The...
  16. C

    Energy to put space shuttle in orbit

    Homework Statement The space shuttle orbits about 300km above the surface of the Earth. The shape of the orbit is circular and the mass of the space shuttle is 6.8*104kg. The mass of the earth is 6.0*1024kg and the radius of the earth is 6.4 *106m. Calculate the energy needed to put the space...
  17. C

    Root Mean Square

    Homework Statement An AC generator produces a voltage of peak value V. The frequency of rotation of the coil of the generator is doubled. The r.m.s. value of the voltage produced is Homework Equations The answer is V multiplied by \sqrt{}2 but I don't understand why. The Attempt at...
  18. C

    Lamp brightness in circuits

    I'm looking at a problem where a battery of negligible internal resistance is connected to two lamps L and N in parallel with each other, then through in series to a 3rd lamp M. The question asks if the filament of one of the lamps in parallel N breaks then what happens to the brightness of the...
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