Kinematics Final Velocity Question

  • Thread starter SkiingAlta
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  • #1
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Hi all. New to the forums. Rookie to Physics. I know this is a really simple question, but I am struggling with it. Help would be greatly appreciated.

Q: Determine the displacement of a plane that experiences uniform acceleration from 66 m/s to 88 m/s in 12s.



Wouldn't I use: Vf^2=Vi^2+2ad

Assuming, this is the correct equation to use what would be the a) Initial Velocity; b) Final Velocity; c) acceleration; and d) distance/displacement?




I am pretty well stuck. Help would be appreciated. Thanks.
 

Answers and Replies

  • #2
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This equation is fine to use, but you will have to solve for acceleration (you have the initial and final velocities, plus the time!) Once you solve for acceleration, you can solve for the displacement over time.
 
  • #3
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Okay, so to find acceleration, I used Vf=Vi+at

Setting the Vf as 88 and the Vi as 68.

Algebraically solving the equation, I found the acceleration to be 1.67. I then plugged into Vf2=Vi2+2ad

Getting my result, 934.13 meters. Is this correct?
 
  • #4
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Is the initial velocity 66 or 68 m/s? If it is 68 m/s, your answer is very close to mine---I'm sure just rounding differences. Just double check the problem.
 
  • #5
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Excuse me. It's 68. Great, thank you so much for your help.
 
  • #6
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Glad you understand it!
 
  • #7
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One more question if you can help:

You throw a ball downward from a window at a speed of 2.0 ms. How fast will it be moving when it hits the sidewalk 2.5m below?

Simple enough right? So my question is.... is it the initial velocity or final velocity that is 2.0? Wouldn't it be initial because it's the final velocity you're trying to find?
 
  • #8
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exactly! 2 m/s would be the initial velocity.
 
  • #9
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Sweet, so technically, since that is "gravity" withheld, the acceleration would be -9.8?
 
  • #10
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also correct! acceleration is -9.8 m/s2.

something to think about--what is the direction of the velocity?
 
  • #11
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What is the direction of the velocity? Well I guess it doesn't really matter as long as its constant... i/e, you could call acceleration +9.8 as long as Vi was -2.0... Is that what you mean?
 
Last edited:
  • #12
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because the velocity is downward it is negative, as well as the acceleration. you can't interchange them. it is just important to note the direction of the velocity depending on the equation you decide to use!
 
Last edited:
  • #13
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Oh duh. Lol. Thanks... I don't process information well at night. Haha. Thanks for the help, I really appreciate it. G'night to ya!
 
  • #14
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very happy to help:D
 

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