1. Limited time only! Sign up for a free 30min personal 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!

Homework Help: Basic Mechanics Problem(2D Motion)

  1. Oct 13, 2007 #1
    Yeah, I pretty much spent 5 hours today trying to figure this question out, yet for some reason I keep getting the wrong answer. I told my friends I'd do it and explain it to them, but I still can't do it right. Can some one please show me the steps using only the letters, not just numbers. Thanx.

    A projectile is launched into the air from the top of an incline that makes an angle f =39° with the horizontal as show in the diagram below. The launch speed, v, is known to be 10.0 m/s but the launch angle, q, is unknown. However, the maximum height above the launch level that the projectile reaches is known to be h = 2.51 m. The trajectory is a perfectly parabolic. What is the angle, a (in degrees), with which the projectile strikes the incline (measured relative to the incline as shown)? Use g = 9.80 m/s2.
    (I dunno if the picture works, but give it a shot)

    2. Relevant equations

    Basic Motion Equations
    Vf = Vi + A(D)T
    (D)X = Vi(D)T + (A(D)T^2)/2
    Vf^2 = Vi^2 + 2A(D)X
    (D) is Delta
    I know Calculus, but my friends don't yet.

    (I would right down one of my attempt, but it would take way too long!)
    I understand how you're supposed to do it(break it up horizontally and vertically) and whatever else(ex: hor. vel. doesn't change, but vert. does due to gravity), but for some reason all the things I tried never gave me the right answer. I filled nearly five pages of stuff!
    Basically, I seperated the problem into four points each with their x and y values(position, velocity, acceleration) and the change in time at each one. Using the 3 equations I'm able to find all the other data, but for some reason I keep messing up no matter what way I do it. I'm certain that q = arcsin(((root)2AH)/10), but I mess u psomewhere along the line. So yeah, any help would be great.
  2. jcsd
  3. Oct 13, 2007 #2
    I did this quickly, so you should double check, but I think your equation is close to correct but not quite. Should it be divided by 100 instead of 10? I think you originally had (10sinq)^2, so don't you have to square the 10 as well as the sinq? (Remeber, I could be wrong).
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook