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  1. S

    Physics: Post your doubts here!

    19) Take the load on the right-hand side string. Since that load is in equilibrium, the tension force on it has to be equal to it's weight, which we are given is 100 Newtons. Now take the scale on the right. The scale will tell us how hard the string is pulling on it, which is the definition...
  2. S

    Physics: Post your doubts here!

    Q10) This is a tricky one at first glance, but a little thought helps clear up things. The sand is dropped horizontally into the cart, so it has no initial horizontal momentum. The cart has some momentum in the beginning, since it is moving initially. Suppose you take the sand and the cart...
  3. S

    Physics: Post your doubts here!

    For M/J/13 - 12: 3) The point where the net force can be assumed to act is the point where the net force will exert the same torque as the single forces taken one by one - suppose I have 3 forces A, B and C acting on a door. The apparent line of action of the net force will be the place where...
  4. S

    Physics: Post your doubts here!

    Hopefully this link helps, and the file attached should also make matters clear - if not, there's this little summary here: "When you multiply or divide a set of number to obtain a product, the number of significant figures quoted in the product should be the same as that of the number with the...
  5. S

    Physics: Post your doubts here!

    I think I did Question 19 here, just let me know if you've got it (if you still have doubts, no issues, let me know!). I'll do the others after a few minutes, have a little work to do elsewhere ;).
  6. S

    Physics: Post your doubts here!

    Yes, ρ = (R Ω) m, but those are a matter of units - the units for the final answer will be in Ωm, which are the units of resistivity (and it should be no other way, to be honest) but that's where the question becomes very specific - it states: ".....resistivity of a material is numerically...
  7. S

    Physics: Post your doubts here!

    Sorry for the late reply, wasn't online for quite some time. Let's take this option by option, with the following formula in focus: ρ = RA/l Where ρ = resistivity of the material through which current is being passed, R = resistance of the sample through which current is being...
  8. S

    Physics: Post your doubts here!

    Q12) Q28) Wow, this is a toughie! Suppose you have two sources of light, beside each other and projecting light onto a screen equidistant from them. This is an alternative set-up to a double slit experiment, where two slits are small enough to act as light sources on their own, and...
  9. S

    Physics: Post your doubts here!

    Since both wires are made of steel, they have the same Young's Modulus value (which is a measure of how easy it is to stretch or compress the material, and is a property of the material itself, not a sample - so, any two pieces of the same material will have the same Young's Modulus). The...
  10. S

    Physics: Post your doubts here!

    When the stone is thrown and in the air, the only force acting on it is gravity, acting vertically downwards. Therefore, the net force F on the stone is also downwards and has a magnitude of (mg) Newtons. By Newton's Second Law, since the net force F is downwards, the acceleration of the stone...
  11. S

    Physics: Post your doubts here!

    We have to look quite hard to get the answer - why does the current seem to prefer the train rather than the relay? Note that a relay should have a low resistance to ensure maximum current flowing through it (and this causes the electromagnetic effect that turns the switch on or off). So if...
  12. S

    Physics: Post your doubts here!

    Since the area under the curve on the Force-extension graph is the energy stored in the spring, you can split the graph into two parallelograms (as in the image attached), and using the formula for calculating area of parallelogram (area = 0.5 * distance between parallel sides * (sum of lengths...
  13. S

    Physics: Post your doubts here!

    Let us take the components of the forces acting on the door in the vertical and horizontal directions: In the vertical direction, the force of gravity acts downwards (written as W), the vertical component of the hinge force H acts downwards (component written as Hv) and the vertical component...
  14. S

    Physics: Post your doubts here!

    Q4) On an oscilloscope screen, the height (or y-gain) displays the voltage of the signal and the x-axis/ x-length displays time. So, taking the wave X, we can see that the peak of the wave is 3 squares above the base-line (the point right in between the crest and the trough). We are also...
  15. S

    Physics: Post your doubts here!

    Ummm....o_O where did I write that? Gravity always acts downwards for objects on Earth or any other spherical surface, so i'm not sure where I wrote that bit.
  16. S

    Physics: Post your doubts here!

    There's some very tight wording there, so just want to confirm: When the force of gravity itself does negative work, the kinetic energy decreases. This is correct. However, when work is done against the force of gravity, it implies there is some force opposing gravity (suppose you are lifting...
  17. S

    Physics: Post your doubts here!

    When a total amount of work W is done on any object, the kinetic energy of that object changes by a quantity W - if negative work is done on the object, the kinetic energy changes by a negative amount and if positive work is done on the object it's energy changes by a positive amount. Suppose...
  18. S

    Physics: Post your doubts here!

    Q25) Two ways of doing this - first, using gradients at a point, and second, using frame-shifts. Let's do the second way first. You know the wave is going from left to right - the question tells you that. Now suppose you take the wave you have now, and mentally shift it very slightly to the...
  19. S

    Physics: Post your doubts here!

    Wow, no idea on 5. However, I did manage to find out something: Between each level (100 to 1000, 1000 to 10000, etc) there is a block of height 0.6 cm - this does not correspond to a linear increment, i.e. this does not mean an increase of 500 ohms, or something like that - the distances on the...
  20. S

    Why not? ;-)

    Why not? ;-)
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