Instantaneous Velocity of a electron with a provided formula

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Homework Help Overview

The problem involves determining the instantaneous velocity of an electron based on its position function x(t) = pt^3 + qt^2 + r, with specific values for p, q, and r. The original poster seeks to find the velocity at various time points but initially uses an incorrect formula for velocity.

Discussion Character

  • Conceptual clarification, Assumption checking, Exploratory

Approaches and Questions Raised

  • Participants discuss the incorrect application of the formula v = x/t and suggest that calculus is necessary for finding instantaneous velocity. Some question the original poster's understanding of derivatives and calculus.

Discussion Status

There is ongoing exploration of the correct approach to finding instantaneous velocity, with some participants providing hints about the need for calculus and derivatives. The original poster expresses uncertainty about their calculus knowledge, while others confirm that derivatives are essential for solving the problem.

Contextual Notes

The original poster indicates that they have not yet learned how to take derivatives in their calculus course, which may limit their ability to apply the necessary concepts to the problem.

Flinze
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Homework Statement


The motion of an electron is given by x(t)=pt^3 +qt^2 +r, with p = -1.9 m/s^3 , q = +1.3 m/s^2 , and r = +9.0 m.

What is the velocity at: a) t=0s b) t=1s c) t=2s d t=3s

Homework Equations


v=x/t

The Attempt at a Solution


I have tried plugging in the time to equal to t, in which for a) i got +9 b)8.4 c)-1 d)-30.6
At this point I'm not sure what to do, and I'm totally lost...
 
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Flinze said:

Homework Statement


The motion of an electron is given by x(t)=pt^3 +qt^2 +r, with p = -1.9 m/s^3 , q = +1.3 m/s^2 , and r = +9.0 m.

What is the velocity at: a) t=0s b) t=1s c) t=2s d t=3s

Homework Equations


v=x/t

The Attempt at a Solution


I have tried plugging in the time to equal to t, in which for a) i got +9 b)8.4 c)-1 d)-30.6
At this point I'm not sure what to do, and I'm totally lost...

Whoever told you that v = x/t? That is almost always false! That is why Newton (or maybe Leibniz) invented calculus, and why you had to learn it.
 
Ray Vickson said:
Whoever told you that v = x/t? That is almost always false! That is why Newton (or maybe Leibniz) invented calculus, and why you had to learn it.

Would it be v=d/t?
 
Flinze said:
Would it be v=d/t?
You're overlooking some obvious hints here.
1. instantaneous velocity
2. calculus
 
you are probably talking about v=dx/dt
 
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I haven't learned how to take derivatives yet using Calculus, my Calculus course just started and we haven't covered much so far. Is there possibly another way of solving this without the use of Calculus?
 
i don't think so o_O
that is really weird... you teachers should be more carefull.. you sure you didn't even touched derivatives while learning kinematics?
 
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WrongMan said:
i don't think so o_O
that is really weird... you teachers should be more carefull.. you sure you didn't even touched derivatives while learning kinematics?

100% we haven't yet... This and another question that is also part of my assignment asks the same thing..
 
Okay, I searched up on YouTube on how to take derivatives, so I took the derivative of my equation in which it becomes x'(t)=3pt^2+2qt+0. Afterwards I plugged in the time into the t's and got my answer! Thanks WrongMan by helping me "accidentally" find what derivatives are when I tried searching up the meaning of v=dx/dt
 

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