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Solve this linear equation

  1. Oct 9, 2009 #1
    1. I thought I was doing it right, but Quest said I have to wrong answer. Can some one solve it in steps and produce a final answer so I can compare?

    Tan 58=(vi-ayt)/axt

    where vi=5.6
    ay=-9.8
    ax=2.1

    solve for t.

    I got 0.87 for t.




    Thank you.
     
  2. jcsd
  3. Oct 9, 2009 #2
    Could you please include your attempt to a solution?
     
  4. Oct 9, 2009 #3
    vi-at=tan 58 (at)
    -(-9.8)t=tan58(2.1)t-5.6
    9.8t=3.36t-5.6
    6.44t=-5.6
    t=0.87
     
  5. Oct 9, 2009 #4
    Take a look at the second to last step. You have:

    6.44*t = -5.6

    Your answer should be negative.
     
  6. Oct 9, 2009 #5
    How do we have negative time though? (its the math to a physics problem)
     
  7. Oct 9, 2009 #6
    Does your problem require you to be in degrees or radians?
     
  8. Oct 9, 2009 #7
    Degrees, and my calculator was set on degrees.
     
  9. Oct 9, 2009 #8
    Maybe you should post the original physics problem. Is it possible you made an error setting the problem up :eek:?
     
  10. Oct 9, 2009 #9
    Initially (at time t = 0) a particle is moving vertically at 5.6 m/s and and horizontally at 0 m/s. The particle accelerates horizontally at 2.1 m/s2 . The acceleration of gravity is 9.8 m/s2 . At what time will the particle be traveling at 58◦ with respect to the horizontal?
     
  11. Oct 9, 2009 #10
    Sorry, I was not aware that 't' is time.
     
  12. Oct 9, 2009 #11
    Oh, it is very possible, ha ha. I am not good at this stuff at all.
     
  13. Oct 10, 2009 #12

    Mark44

    Staff: Mentor

    At t = 0, is the thing moving up or down? If it's moving up, vi will have a sign opposite to that of gravitational acceleration. Your equation in the first post suggests that the thing is moving up.
     
  14. Oct 10, 2009 #13
    I assume you are using equations for constant acceleration. You are going to need to break your equations into components: one for your vertical velocity and acceleration components and one for your horizontal components.

    Vy=Viy+ay*t
    and
    Vx=Vix+ax*t

    Where
    Vy=V*sin(58)
    Vx=V*cos(58)

    You end up with two equations and two unknowns (V and t). You should be able to solve.
     
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