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Very important physics TEST

  1. Jun 7, 2008 #1
    Hey guys, next week I'm writing a very important test, so it would really help me if someone could solve the exercises. Here it is:

    Attached Files:

  2. jcsd
  3. Jun 7, 2008 #2


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    Welcome to PF!

    Hi croatia_guy ! Welcome to PF! :smile:

    Your attachment won't show up for several hours.

    Would you like to describe the problem now?

    And remember, you have to show us what you've done, so that we know how to help you. :smile:
  4. Jun 7, 2008 #3
    ok, there are 4 questions in each group and i wasn't in school for a long time, like 3 weeks, and i don't understand anything.
    A group

    1. A 20-kg stone is thrown downwards at 12 m/s from the top of the ESB. The ESB is 450 m high. The force of air friction is 120 N. Find the impact velocity of the stone to the ground.
    2. A certain planet has a mass of 2*10 on the 26 kg and its radius is 20 000 km. Find when a bat will reach the altitude of 2m if it is launched vertically up at 90 m/s on this planet. (G= 6.67*10 [-11]Nm [2] kg [-2])
    3. A bomber flies at unknown velocity at 1.5 km over the London. A bomb is dropped and it will strike the ground 1.8 km far. Find the velocity of the bomber.
    4. When a ship steams upstream, its velocity is 12 km/h. If the velocity of the river stream is 20 km/h , what the velocity of the ship will be when it steams downstream?

    B group

    1. A 600-kg mad bull strikes at 5 m/s thin wooden plate. The bull passes through the plate. Find the velocity of the bull after passing if the plate is 20 cm thick and thw force of 500N is required to break the plate.

    2. A stone is thrown vertically up at 80 m/s. Find the velocity and the altitude in 2.4 s.

    3. A javelin is thrown horizontally at 20 m/s from a 140 m high tower on a certain planet (R= 7000 km, M= 9 * 10 [24]kg). Find the horizontal range of the javeline (G= 6.67 * 10 [-11] Nm[2]kg[-2]).

    4. A bomber travels 400km in 1.2 h from France to Dresden. If the velocity of the tail wind is 50 km/h what is real velocity of the bomber?

    Numbers in this [] are those little numbers which are written near ''big'' numbers... You know what I mean. Sorry, but i don't know how to explain it in English.
  5. Jun 7, 2008 #4


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    (btw, the little number is called the "index" … you can make it little, like this, by using the Size tool on the Reply page)

    ok … use energy.

    You have the initial KE, you know the gravitational PE lost, and you can calculate the energy lost to friction by using Work (force times distance = work = energy lost).

    Add or subtract them to get the final KE.

    Have a go! :smile:
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