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Homework Help: Can someone double check my answers to this practice exam?

  1. Oct 10, 2015 #1
    1. The problem statement, all variables and given/known data


    2. Relevant equations

    basically just kinematics, projectile motion, and force equations.

    3. The attempt at a solution

    I got :
    1. either B or D
    2. D
    I was using this practice exam to study but quickly realized there were no answers posted, so I'm unaware if what i'm doing is correct..
    Thank you!!
  2. jcsd
  3. Oct 10, 2015 #2


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    I get different answers for 1, 10, 11, 13, 14, 16.
  4. Oct 10, 2015 #3
    thank you!
  5. Oct 10, 2015 #4
    okay, so for 1. I think it's B because A cant be true since part of the slope is negative and thus negative velocity. C can't be true because at t=1 the velocity is positive, and t=7 the velocity is negative. D can't be true because the acceleration is zero at that point because the position plot is a line without a changing slope. E can't be true because at t=6, the ball has a negative velocity.

    Now ,
    10. The helicopter goes up 1000 m. Now it begins to move 45 degrees at an acceleration of 2 m/s^2 for 30 seconds.. so final velocity= 2(30). to find avg velocity, i did (vfinal-vinitial)/2 which brings us to 30. so 30 m/s * 30 seconds = 900 ft..so i did 900+1000 = 1900..i think i went wrong somewhere calculating velocity because Vinitial might not have been 0 as the copter was already in motion but idk how to find vinitial..

    11. i dont even know how to approach this question. i suppose its something to do with projectile motion definitions.. maybe to do with the the independence of x and y components

    13. Now i got D. i got this because i re-read the question, it says "relative to the water", so I just divided .20 km by 8 m/s to see how long it would take.

    14. I got D, i just added the components of the two forces and solved for magnitude.

    16. now i got B, realized i plugged into equation incorrectly..
  6. Oct 10, 2015 #5
  7. Oct 10, 2015 #6
    okay so..
    10. found it somewhere online. i was calculating it where it was 1000 feet straight up and then 900 ft in a direction that was 45 degrees clockwise to that, but apparently it's supposed to be a 90 degree turn then 900 feet. so then its just sqrt(1000^2+900^2)=1350 (A)
    11. Okay, so h=1/2gt^2. so as max height increases, so does time in air. this means that C must be correct!
  8. Oct 11, 2015 #7


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    All good now except for 13.
  9. Oct 11, 2015 #8


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