Finding Values of A, B, and C for Parabolas on a Velocity-Time Graph

In summary, at t=0, the velocity is zero and the slope is zero; at t=6, the velocity is 20 and the slope is -5/4; at t=8, the velocity is 50 and the slope is -5/4; and at t=10, the velocity is 100 and the slope is -50.
  • #1
AlchemistK
158
0

Homework Statement



The graph in the attached file is a velocity-time graph.
We have to find the total displacement from t=0 to t=10.

I know that integration will be used for this problem, and i know my formulas but i do not know of how to form the equation of the two parabolas here.
I know it is of the form Ax^2 + Bx + C but how do i figure out the A.B and C?
 

Attachments

  • untitled1.bmp
    47.1 KB · Views: 504
Physics news on Phys.org
  • #2
Since you know some of the values that the parabolas pass through you can set up a series of equations with know Y and X values and solve for A, B, and C
 
  • #3
AlchemistK said:

Homework Statement



The graph in the attached file is a velocity-time graph.
We have to find the total displacement from t=0 to t=10.

I know that integration will be used for this problem, and i know my formulas but i do not know of how to form the equation of the two parabolas here.
I know it is of the form Ax^2 + Bx + C but how do i figure out the A.B and C?
Look at the bottom-left parabola v = a + b*t + c*t^2. Looking at the graph, what is the value of v when t = 0? What does that say about a, b and c? What is the slope of the graph v at t = 0? What does that say about a, b and c? Finally, you have another point on the graph. That tells you more about a, b and c. You now have enough to determine the graph completely. Do something similar for the right-hand parabola, namely: use the fact that you have three points on the graph, so you can determine the three constants.

RGV
 
  • #4
Ray Vickson said:
Look at the bottom-left parabola v = a + b*t + c*t^2. Looking at the graph, what is the value of v when t = 0? What does that say about a, b and c? What is the slope of the graph v at t = 0? What does that say about a, b and c? Finally, you have another point on the graph. That tells you more about a, b and c. You now have enough to determine the graph completely. Do something similar for the right-hand parabola, namely: use the fact that you have three points on the graph, so you can determine the three constants.

RGV
At t = 0, the velocity is 0 and so is the slope, right? And i forgot to mention but the initial velocity is 0 so, the equation for the parabola there should be cx^2 because the vertex is at the origin.
Putting the values of 3 and 5 in the equation, c comes out to be 5/4.
The area of the bottom left curve after integrating, if i am not wrong, comes out to be 10/3.

Am i correct?
 
Last edited:
  • #5
Looks right to me. Now what about the 2nd parabola? Another method you can try is putting it in vertex form since you can see where the vertex is, do you remember how to do that?
 
  • #6
Clever-Name said:
Looks right to me. Now what about the 2nd parabola? Another method you can try is putting it in vertex form since you can see where the vertex is, do you remember how to do that?

By using the equation of parabola (ax^2 + bx +c) on the three give points at t=6,8 and 10, i can figure out the values of a,b and c, which are, -5/4 , 20 , -50. Right?
 

What is the purpose of integrating the area under a v-t graph?

The integration of the area under a v-t graph is used to calculate the displacement of an object over a specific time interval. It allows us to determine how far an object has moved, even if its velocity is constantly changing.

How do you integrate the area under a v-t graph?

To integrate the area under a v-t graph, you can use the formula ∫v(t)dt = ∆x, where v(t) is the velocity function and ∆x is the displacement. You can also use the trapezoidal rule or the Simpson's rule for more accurate results.

What units are used for the area under a v-t graph?

The area under a v-t graph represents displacement, which is measured in meters (m). Therefore, the units for the area under a v-t graph are also meters (m).

Can the area under a v-t graph be negative?

Yes, the area under a v-t graph can be negative. This indicates that the object is moving in the opposite direction of the positive displacement. A negative area also means that the object is returning to its original position.

How does the shape of the v-t graph affect the area under it?

The shape of the v-t graph directly affects the area under it. A straight line (constant velocity) results in a rectangular area, while a curved line (changing velocity) results in a trapezoidal area. The steeper the slope, the greater the velocity and therefore the larger the area under the graph.

Similar threads

  • Introductory Physics Homework Help
Replies
6
Views
725
  • Introductory Physics Homework Help
Replies
2
Views
2K
  • Introductory Physics Homework Help
Replies
7
Views
378
  • Introductory Physics Homework Help
Replies
14
Views
3K
  • Introductory Physics Homework Help
Replies
5
Views
267
  • Introductory Physics Homework Help
Replies
25
Views
1K
  • Introductory Physics Homework Help
Replies
5
Views
672
  • Introductory Physics Homework Help
Replies
7
Views
851
Replies
44
Views
1K
  • Introductory Physics Homework Help
Replies
14
Views
2K
Back
Top