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Projectiles thrown at an angle

  1. Oct 17, 2006 #1
    i'm having a lot of trouble with these:

    1. A golf ball with an initial angle of 36° lands exactly 210 m down the range on a level course.
    (a) Neglecting air friction, what initial speed would achieve this result?

    (b) Using the speed determined in item (a), find the maximum height reached by the ball.

    2. A science student riding on a flatcar of a train moving at a constant speed of 5.00 m/s throws a ball toward the caboose along a path that the student judges as making an initial angle of 65.0° with the horizontal. The teacher, who is standing on the ground nearby, observes the ball rising vertically. How high does the ball rise?

    if anyone knows how to do these, help would be amazing. thanks!
     
  2. jcsd
  3. Oct 17, 2006 #2

    radou

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    Homework Helper

    Here, this should be useful: http://www.ac.wwu.edu/~vawter/PhysicsNet/Topics/Vectors/ProjectilesMotion.html.

    After showing us some of your work, we'll be glad to jump in if necessary.
     
  4. Oct 17, 2006 #3

    (a) Use the range equation: [tex]X_f[/tex] - [tex]X_i[/tex] = [tex]\frac{V_i^2sin(2\theta)}{g}[/tex]
     
    Last edited: Oct 17, 2006
  5. Oct 17, 2006 #4
    The range of a projectile (how far it travels) is given by the equation
    v2sin2@/g

    note: i unconventionally used @ for the angle

    The height is given by
    h=v2sin2@/2g

    These equations are derived from the basic kinematic equations of projectile motion under constant acceleration, have fun!
     
  6. Oct 17, 2006 #5
    thanks a lot for all the help, i got the first question. i'm still stuck on the second one, and what's worse is that i have another one:

    A car is parked on a cliff overlooking the ocean on an incline that makes an angle of 24.0° below the horizontal. The negligent driver leaves the car in neutral, and the emergency brakes are defective. The car rolls from rest down the incline with a constant acceleration of 6.50 m/s2 and travels 50.0 m to the edge of the cliff. The cliff is 40.0 m above the ocean.
    (a) What is the car's position relative to the base of the cliff when the car lands in the ocean?

    (b) How long is the car in the air?

    i don't know if something's wrong with me because i can calculate upward angles, but downward angles won't work the same way.
     
  7. Oct 17, 2006 #6
    thanks a lot for all the help, i got the first question. i'm still stuck on the second one, and what's worse is that i have another one:

    A car is parked on a cliff overlooking the ocean on an incline that makes an angle of 24.0° below the horizontal. The negligent driver leaves the car in neutral, and the emergency brakes are defective. The car rolls from rest down the incline with a constant acceleration of 6.50 m/s2 and travels 50.0 m to the edge of the cliff. The cliff is 40.0 m above the ocean.
    (a) What is the car's position relative to the base of the cliff when the car lands in the ocean?

    (b) How long is the car in the air?

    i don't know if something's wrong with me because i can calculate upward angles, but downward angles won't work the same way.
     
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