H2 physics questions

• Audi

  13 Jan 11, 22:47

  Ok a handful of questions which I am unsure of.

  1. A satellite is moving in a circular orbit around Earth. A piece of it becomes detached. Assuming that air resistance can be neglected, this piece will

  A move directly away from Earth

  B fall directly towards the Earth

  C continue to move in a circular path

  D continue to move along a tangent to the orbit.

  2. When a gun is fired from a stationary aeroplane, the bullet has a speed v and a kinetic energy K. The gun is again fired, straight ahead when the plane is flying at a speed equal to v. The kinetic energy of the second bullet is

  A    K   B (2K)^0.5     C 2K     D 4K

  I chose K, but I am unsure about it. (l was thinking abt sth along the lines of internal energy althou this is NOT a question related to I.E, but i think being on a plane does not affect K.E of the bullet? well, no idea).

  3 R is the electrical resistance measured btw the ends of a cylindrical conductor of radius r. If a hole of r/2 is drilled along the axis of the cylinder from one end to the other, the new resistance will be

  R/4     R/2      4R/3     3R

  I found that the resistance of the SMALLER and drilled wire is 4x MORE than the original cylinder. So original cylinder is R, smaller and drilled one is 4R. the remaining resistance of the leftover cylinder should be R<ans<4R. So the ans is either 4R/3 or 3R. But I dont know how to proceed further from here.

  4. Which of the following statements is true for the motion of a spherical ball falling from rest thru a homogenous liquid? (simple question but I am uncertain about it, lol)

  velocity decreases as distance fallen increase

  velocity remains constant

  acceleration is constant

  acceleration decreases as distance fallen increases.

  At first I chose the last option, but what are the EFFECTS of being in a homogenous liquid? (Air resistance constant? if thats the case, should i choose the 3rd option instead?)

• wee_ws

  14 Jan 11, 07:00

  Hi,

    You may wish to read this info about homogenous mixture:

    http://en.wikipedia.org/wiki/Solution

    Homogenous therefore suggests uniformity.

    Thanks.

  Cheers,
  Wen Shih

• wee_ws

  14 Jan 11, 07:26

  Hi,

    For Q1, option is D. No net force is exerted on the detached piece and it will now move in a straight line by Newton's first law.

    Thanks.

  Cheers,
  Wen Shih

• wee_ws

  15 Jan 11, 08:17

  Hi,

    In Q2, speed of bullet relative to the ground is 2v. Thanks.

  Cheers,
  Wen Shih

• wee_ws

  15 Jan 11, 08:25

  Hi,

    In Q3, resistance is inversely proportional to area. Thanks.

  Cheers,
  Wen Shih