1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

I NEED major help, its about getting time?

  1. Oct 11, 2006 #1
    How would you get time for this:

    5. A stone is thrown horizontally at 8.0 m/s from a cliff 78.4 m high. How far from the base of the cliff does the stone strike the ground? (Use GUESS Method)

    G: vi = 8.0 m/s
    g = 9.8 m/s2
    dy = 78.4 m
    U: dx
    E: d = vi*t +1/2 a*t^2
    S: dx = 32 m


    vi =initial velocity
    ^2= squared
    *= times
     
  2. jcsd
  3. Oct 11, 2006 #2

    quasar987

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    The motion in the y-direction and in the x-direction are independant, right?

    So first you'll want to use equation "E" to calculate the time is takes the rock to fall the 78.4m. Then, use the time you found in a similar equation, but for the x distance (of course is no acceleration term in equation "E")
     
  4. Oct 11, 2006 #3
    I don't know what the GUESS method is, but the first thing I would do is ignore that any type of horizontal motion exists. I would imagine the stone simply being dropped off the cliff. With the knowlege of the height of the cliff and the fact that it is dropped (vi = 0) you can calculate the amount of time that the stone is in the air. Now I remind myself of this horizontal velocity that the rock was given. To calculate the horizontal distance I just use d = vi*t +1/2 a*t^2. There is no acceleration in the x direction so it is simply D = ViT. You know the initial velocity and you calculated the time.
     
  5. Oct 11, 2006 #4
    ...But how would i get the time, i dont know how to get it?
     
  6. Oct 11, 2006 #5

    PhanthomJay

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    I don't know what the GUESS method is. However, you should note that v_i is 8m/s in the x direction. V_xi =8. There is no initial component of v in the y direction. V_yi = 0. In the x direction, there is no acceleration, so v_x stays constant throughout the trip, therfore, x =v_x(t), this is the horizontal distance traveled. To solve for t, use your the "E" equation in the y direction, where d =78.4 , v_i = 0, and a =9.8. Then solve for x, I guess.
     
  7. Oct 11, 2006 #6
    wow thanks that helped a bit, thanks guys
     
  8. Oct 11, 2006 #7
    I got another one.

    7.A dart player, standing 3.2 m away from the dartboard, throws a dart horizontally at a speed of 12.4 m/s. How far from the bull’s eye (where the player aimed) did the dart strike? (Use GUESS Method)

    G: g = 9.8 m/s2
    dx = 3.2 m
    vi = 12.4 m/s
    U: dy
    E: d = vit +1/2at2
    S: dy = 0.32 m (give a direction)
     
  9. Oct 11, 2006 #8
    need more help fast.??!?!?

    7.A dart player, standing 3.2 m away from the dartboard, throws a dart horizontally at a speed of 12.4 m/s. How far from the bull’s eye (where the player aimed) did the dart strike? (Use GUESS Method)
     
  10. Oct 11, 2006 #9
    I think people on these boards are more familiar with teh ViVfdat method (same sorta thing...)

    again same sorta concept as ur last problem...no initial y velocity...no x acceleration...then just set up a system with the values...knowing that acceleration in y direction is g and then solve...its similar to the last one u did if you got it...just having a different unknown this time...meanign a different equation...

    Vix 12.4
    Vfx 12.4
    Dx 3.2
    ax 0
    t = t

    Viy = 0
    Vfy = ?
    dy = x
    ax = -g
    t = t

    whats the only common variable between the two sets?
     
  11. Oct 11, 2006 #10
    umm.... is that guna be t?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?