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Projectile Motion- Please Help me

  1. Mar 15, 2007 #1
    1. 1) What is the maximum possible speed of impact upon the surface of the Earth for a faraway body initially at rest that falls to the Earth by virtue of the Earth's gravity only?

    2) A ball is thrown horizontally from a cliff at a speed of 11 m/s. What is its speed one second later?

    3) An airplane is flying horizontally with speed 1000 km/h (280 m/s) when an engine falls off.
    (a) Neglecting air resistance, if it takes 30 s for the engine to hit the ground how high is the airplane?

    (b) If it takes 30 s for the engine to fall how far horizontally does the engine travel while it falls?

    (c) If the airplane somehow continues to fly as if nothing had happened, where is the engine relative to the airplane at the moment the engine hits the ground?

    (multiple choice)
    a) directly below the plane
    b) in front of the plane
    c) behind the plane

    4) Students in lab measure the speed of a steel ball launched horizontally from a table top to be 3.4 m/s. If the table top is 1.5 m above the floor, where should they place a 20 cm tall tin coffee can to catch the ball when it lands?

    5) John and Tracy look from their 71 m high-rise balcony to a swimming pool below - not exactly below, but rather 17 m out from the bottom of their building. They wonder how fast they would have to jump horizontally to succeed in reaching the pool. What is the answer?

    6) Ignoring air drag, what is the maximum speed possible for a horizontally-moving tennis ball as it clears the net 1.5 m high and strikes within the court's border, 12.0 m distant.

    7) Calculate the speed in m/s at which the Earth revolves about the sun. You may assume the orbit is nearly circular.

    8) A satellite is about 1.8 103 km from the (center of the) Earth. Find its average orbital speed about the Earth.

    2. I'm sorry but i dont know, thats why i'm so confused, these were on www.webassign.com I don't know what formulas to use....

    3. umm.... i'm sorry, i don't want this deleated, i have no clue how to solve it... i've been trying and i'm sooo lost, oh and it's due in less then an hour so i dotn know what to do, could someone explain this to me??
    Last edited: Mar 15, 2007
  2. jcsd
  3. Mar 15, 2007 #2


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    Homework Helper
    Gold Member

    You really must show some work. It is the rules. You can't be COMPLETELY lost on every one?

    Some hints to help you along your way:

    1) Consider the change in poetential energy for an object very far away( at infinity) that hits the earth. This must equal the change in kinetic energy correct?

    2) Speed in x direction won't change, find the new y speed and ten add the vectors.

    3) a)Worry only about the y motion.

    b) answer from a) is needed

    c) what is the horizontal acceleration
    4)5)6) All three are projectile motion problems. consider the horizontal and vertical motion separately.
    7) See number 8
    8) Force of gravity = Centripetal Force

    This should help get you started. I'm sorry but it is our policy not to DO HOMEWORK for someone. Considering this rule, I'll give you these hints. They should help get you started.

    Good Luck!
    Last edited: Mar 15, 2007
  4. Mar 15, 2007 #3
    thanks for the help, and i am lost on all of these, i started with 26 questions, these were the ones i couldnt get
  5. Mar 15, 2007 #4


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    Homework Helper
    Gold Member

    No problem.....I added some more small hints........
  6. Dec 8, 2007 #5

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