Vectors and Trigonometry Homework Help

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Homework Help Overview

The discussion revolves around a physics problem involving projectile motion, specifically analyzing the motion of a stone thrown vertically with an initial speed. Participants are examining the time it takes for the stone to reach a certain altitude and the corresponding velocity at that height.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants are discussing the use of kinematic equations to determine the time and velocity of the stone at a specified height. There is a focus on whether the problem has one or two possible answers, prompting questions about the nature of the quadratic equation involved.

Discussion Status

The discussion is ongoing, with some participants offering guidance on solving quadratic equations and others expressing uncertainty about their calculations. There is no explicit consensus on the correct approach yet, but there are indications of productive engagement with the problem.

Contextual Notes

Participants have noted discrepancies between their calculated answers and the expected results, highlighting potential misunderstandings in applying the relevant equations. There is also a request for more detailed workings to identify errors in reasoning.

Lui4
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Homework Statement
A stone is thrown straight up with a speed of 15.0m/s
(a) How fast will it be moving when its altitude is 8.0m above the point from which it was thrown? How much time elapses while the stone is reaching that height?
(b) Is there one answer or are there two answers? Why?
Relevant Equations
D=vot+(1/2) (a) (t)^2
Hey, I am new to this community and I am in need of help with this physics problem. I have used the formula above and the answer I get is 1.43s. The correct two answers are 0.68s and 2.4s. For the Vf the answer is 8.3 m/s.
 
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Lui4 said:
Homework Statement:: A stone is thrown straight up with a speed of 15.0m/s
(a) How fast will it be moving when its altitude is 8.0m above the point from which it was thrown? How much time elapses while the stone is reaching that height?
(b) Is there one answer or are there two answers? Why?
Relevant Equations:: D=volt+(1/2) (a) (t)^2

Hey, I am new to this community and I am in need of help with this physics problem. I have used the formula above and the answer I get is 1.43s. The correct two answers are 0.68s and 2.4s. For the Vf the answer is 8.3 m/s.
If you would like someone to point out where you went wrong it would be helpful if you were to post your working.
 
Hey, thanks for the quick reply. Hope this helps understand the problem better!

1607937531507.png

1607937606153.png


1607937567714.png
 
You don't seem to know how to solve quadratic equations.
 
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Oh, okay.
 
A guide on how to solve a quadratic equation Quadratic equation - Wikipedia

If you are bored to read all that (lol) here is the core of that article:
A quadratic equation ##ax^2+bx+c=0## has (in the most general case) two roots:
$$x_1=\frac{-b+\sqrt{b^2-4ac}}{2a}$$ and $$x_2=\frac{-b-\sqrt{b^2-4ac}}{2a}$$
 
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Thank you for your help, I’ll keep this in mind when looking at the question!
 
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