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Homework Help: Help! impossible (yet basic?) physics questions

  1. Nov 2, 2003 #1
    hi all... here are some physics questions that i am puzzled on and lost. help! if you are able to solve them please show how, or at least what formulas/equations you used to get there. thanks! (even if you have a clue take a shot!anything could help).

    when a 0.64kg ball is dropped on your hand from 0.73m above it, your hand recoils 2.4cm before stopping. what is the average force on your hand while stopping the ball?

    the average density of the planet mercury is 5.61x10^3 kg/m^3. the acceleration due to gravity is 3.92 m/s^2. calculate the average radius of mercury.

    gold has a density of 1.74x10^3 kg/m^3. calculate the gravitational field strength 10m from a 1m cube of gold.

    the 3.56g bullet from a 22-250 rifle is fired vertically into a 1.174kg block of wood. the bullet sticks to the block, which rises 0.595m. what was the speed of the bullet at impact?

    what is the total energy stored in 1 kg of water?

    if an astronaut dropped a small rock on the surface of mars, how far would it fall in 1.00 seconds? the mass of mars is 0.107 that of earth and the radius of mars is 0.53 that of earth.

    an egg falls from a height of 3.0m. what speed will it have when it is 0.5m from the ground?

    calculate the mass of jupiter from the information that its moon Io orbits at an average distance of 4.22x10^5km from jupiter's center and has an orbital period of 42.5 hours.

    what would be the orbital period of an earth satellite that orbits 1/3 the distance to the moon?

    a spacecraft travelling at 0.8c away from the earth launches a probe that is travelling 0.95c from the spacecraft's frame of reference. what is the speed of the probe from the point of view of the earth?

    what is the acceleration due to gravity 1000km above the surface of the earth?

    any ideas?????
  2. jcsd
  3. Nov 2, 2003 #2

    Chi Meson

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    What is this, your take-home mid-term that's due tomorrow?
  4. Nov 2, 2003 #3
    This is all really basic formula manipulation, did you even try?
  5. Nov 2, 2003 #4
    Post this in the homework forum, with along with your work and you will be helped.

  6. Nov 3, 2003 #5
    beat the instructor

    these questions are challange questions from our teacher (MIT grad) who gave us these knowing that they were a bit out of reach for us as we are a beginning intro physics class(HS). we haven't but scratched the surface on these topics. so we're trying to find/acquire at least a basic, rough understanding so we can say "ah ha. you've not been completely successful in stumping us." because he gets a laugh when we come in and don't have a clue. and he wins. so our whole class is desperately looking for something to show for these problems.
  7. Nov 3, 2003 #6

    thanks for at least trying to help/ redirect me nautica.
  8. Nov 3, 2003 #7

    Chi Meson

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    If this a requirement, and your teacher hasn't taught you any formula manipulation, then your teacher is cruel.

    If your teacher really gets a laugh out of stumpling you, then your teacher is cruel.

    If this is just an exercise to show how amazing physics can be at predicting outcomes, or showing how useful physics is in the real world, then I suppose it's a fair demonstration. But you are right: if you have not been shown the formulas and if the teacher has not demonstrated how to manipulate formulas, some of these problems will be near impossible to solve.

    Here's the egg one: When anything is dropped from a certain height, it will begin with a certain amount of energy called gravitational potential energy. THis amount is calculated as = mass x "g" x height. "g" is the "acceleration due to gravity" (a constant when near the earth's surface, approximately 32 feet per second per second)

    As the egg falls, this potential energy transforms into kinetic energy (the energy of motion) which is calculated as (1/2)x mass x speed squared.

    These two formulas are assumed to be equal to each other since the total amount of energy must remain constant. With formula manipulation we find that speed = square root of (2 x "g" x h).

    And this is the simplest explanation of the whole list.
  9. Nov 5, 2003 #8


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    Fd = mgh

    the formula for gravitational field is something like Gm/d^2. Since we don't know the mass of the planet or the radius, this question cannot be done with the information given.


    (1/2)mv^2 = mgh.

    I don't really know what this question is asking. Does the question mean energy in terms of mass or energy in terms of bond strength? If it's about mass energy, the equation is just E = mc^2. If the question is about bond strength, it's a little more complicated.

    Vf^2 = Vi^2 + 2ad where d is 2.5
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