How do you find the speed in this question?

  • Context: Undergrad 
  • Thread starter Thread starter jlmac2001
  • Start date Start date
  • Tags Tags
    Speed
Click For Summary

Discussion Overview

The discussion revolves around determining the speed and magnitude of acceleration of a particle described by the position function r(t) = i cos(t) + i sin(t) + kt. Participants explore the implications of constant speed and acceleration, the process of differentiation, and the interpretation of motion.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants propose that speed is the magnitude of velocity and suggest finding the first and second derivatives to show that both magnitudes are constants.
  • Others question whether the terms "constant" and "magnitude" imply equality between speed and acceleration, indicating uncertainty about the definitions.
  • One participant asserts that the derivative of r(t) leads to r'(t) = r''(t) - k, suggesting that this indicates non-constancy.
  • Another participant challenges the assertion that speed and acceleration are not constant, arguing that it only shows they are not equal.
  • There is a suggestion that a potential typo exists in the original position function, questioning the use of the unit vector i and proposing that j might be intended for a complete description.
  • One participant clarifies their interpretation of the position function, suggesting a correction to include both i and j unit vectors.

Areas of Agreement / Disagreement

Participants express differing views on whether the speed and magnitude of acceleration are constant, with some asserting they are not equal while others challenge this conclusion. The discussion remains unresolved regarding the implications of the derivatives and the potential typo in the position function.

Contextual Notes

There are unresolved assumptions regarding the definitions of speed and magnitude, as well as the potential impact of the unit vector notation on the analysis.

jlmac2001
Messages
75
Reaction score
0
The position of a particle at time t is given by
r(t)= i cos(t) + i sin(t) + kt
Show that both the speed and magnitude of the acceleration are constant. Describe the motion.

Answer:

Does constant mean they come out to b the same answer? For the speed will I take the derivative of r(t). Or is speed the same as magnitude? To get the magnitude I just the the sqrt of the equation with each element squared? What is the motion?
 
Physics news on Phys.org
The speed is the magnitude of the velocity. Thus you need to find the first and second derivatives, and then you can find their magnitudes, and thus show that both magnitudes are constants (but not necessarily equal to each other).

Yes, you can get the magnitude by adding up the squares of the components and then taking the square root.

"Describe the motion" is just asking you to describe how the particle is moving. Since you have functions for the position, velocity and acceleration, you should be able to do that.
 
Originally posted by jlmac2001
The position of a particle at time t is given by
r(t)= i cos(t) + i sin(t) + kt
Show that both the speed and magnitude of the acceleration are constant. Describe the motion.

Answer:

Does constant mean they come out to b the same answer? For the speed will I take the derivative of r(t). Or is speed the same as magnitude? To get the magnitude I just the the sqrt of the equation with each element squared? What is the motion?


r'(t) = r''(t) - k.

thus is not constant.
 


Originally posted by PrudensOptimus
r'(t) = r''(t) - k.

thus is not constant.

Ummm, that doesn't prove that either of those are not constant. Just that they aren't equal.
 
Originally posted by jlmac2001
r(t)= i cos(t) + i sin(t) + kt
Show that both the speed and magnitude of the acceleration are constant.

I think you've got a typo here. If the only unit vector is i, then the speed will most certainly not be constant. Did you mean for one of them to be j? Also, with which unit vector is the kt to be associated?
 


Originally posted by Tom
I think you've got a typo here. If the only unit vector is i, then the speed will most certainly not be constant. Did you mean for one of them to be j? Also, with which unit vector is the kt to be associated?

I assumed what he was typing was:

\boldsymbol{r}(t)=\boldsymbol{i}\cos t+\boldsymbol{j}\sin t+\boldsymbol{k}t
 

Similar threads

  • · Replies 7 ·
Replies
7
Views
813
  • · Replies 8 ·
Replies
8
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 14 ·
Replies
14
Views
5K
  • · Replies 8 ·
Replies
8
Views
3K
Replies
16
Views
2K
  • · Replies 29 ·
Replies
29
Views
5K
  • · Replies 42 ·
2
Replies
42
Views
3K
  • · Replies 6 ·
Replies
6
Views
2K
Replies
60
Views
5K