Kinematics Final Velocity Question

In summary, a new member of the forum is seeking help with a physics problem involving determining the displacement of a plane experiencing uniform acceleration. After discussing the equation to use and solving for acceleration, the conversation shifts to another problem involving a ball being thrown downward. The direction of the velocity and its effect on the equations is also discussed, with the conclusion that the velocity and acceleration are both negative due to the downward direction. The summary ends with the member thanking the expert for their help and wishing them goodnight.
  • #1
SkiingAlta
19
0
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.
 
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  • #2
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
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
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
Excuse me. It's 68. Great, thank you so much for your help.
 
  • #6
Glad you understand it!
 
  • #7
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
exactly! 2 m/s would be the initial velocity.
 
  • #9
Sweet, so technically, since that is "gravity" withheld, the acceleration would be -9.8?
 
  • #10
also correct! acceleration is -9.8 m/s2.

something to think about--what is the direction of the velocity?
 
  • #11
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?
 
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  • #12
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
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
very happy to help:D
 

What is Kinematics?

Kinematics is the study of motion, including the position, velocity, and acceleration of objects over time.

How do you calculate final velocity?

Final velocity is calculated by adding the initial velocity to the product of acceleration and time. The formula for final velocity is Vf = Vi + at, where Vf is final velocity, Vi is initial velocity, a is acceleration, and t is time.

What is the difference between final velocity and average velocity?

Final velocity is the velocity of an object at a specific point in time, while average velocity is the average of an object's velocity over a specific time interval. Final velocity takes into account changes in acceleration, while average velocity does not.

How does mass affect final velocity?

Mass does not directly affect final velocity, but it can affect the acceleration of an object. Objects with larger masses require more force to accelerate, so they may have a slower final velocity compared to objects with smaller masses.

Can final velocity be negative?

Yes, final velocity can be negative if the object is decelerating or moving in the opposite direction of its initial velocity. The negative sign indicates the direction of motion, not the value of velocity itself.

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