Find magnitude of two velocities, with one at an angle?

In summary, the problem involves using Pythagorean theorem and trigonometry to find the magnitude and direction of a resultant vector. The conversation discusses different approaches and calculations, with the final solution being 68.67 for the magnitude and the need to adjust for the correct direction.
  • #1
Brianna I
8
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Member advised to use the homework template for posts in the homework sections of PF.
Here is the problem:
upload_2016-9-17_16-13-35.png


I am sure I can use pythagorean theorem of quadratic equation to solve but to be honest I'm blanking ridiculously.
I have tried setting it on a coordinate grid and finding the resultant, but I have had no luck! I know I've done this problem before in high school but I'm blanking and have spent a few hours now contemplating this.
Thank you!
 
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  • #2
You could start by breaking up the wind into its x and y components. Remember your trig.
 
  • #3
Kpgabriel said:
You could start by breaking up the wind into its x and y components. Remember your trig.
Hi! I have tried what you said but still do not have the right answer. Here is my work:
upload_2016-9-17_16-54-27.png


Excuse the writing, I'm in a car haha!
 
  • #4
Brianna I said:
Hi! I have tried what you said but still do not have the right answer. Here is my work:
View attachment 106148

Excuse the writing, I'm in a car haha!
Ok, so you found your components for the wind. Now find the components for the glider. look on your graph what angle is the glider traveling?
 
  • #5
Kpgabriel said:
Ok, so you found your components for the wind. Now find the components for the glider. look on your graph what angle is the glider traveling?
Sorry, it looks like you already have the components for the resultant vector. So you should have no problem finding the magnitude by using Pythagorean theorem.
 
  • #6
Kpgabriel said:
Sorry, it looks like you already have the components for the resultant vector. So you should have no problem finding the magnitude by using Pythagorean theorem.
Hi, as you can see I tried that. It did not work :( Do I sum both the x-coordinates? I had 31cos45 - 87 since they are on opposite sides of the coordinate grid.
 
  • #7
Kpgabriel said:
Ok, so you found your components for the wind. Now find the components for the glider. look on your graph what angle is the glider traveling?
Ah, would it be at 180o?
 
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  • #8
Brianna I said:
Hi, as you can see I tried that. It did not work :( Do I sum both the x-coordinates? I had 31cos45 - 87 since they are on opposite sides of the coordinate grid.
Right, what did that give you?
 
  • #9
Brianna I said:
Ah, would it be at 180o?
Yes it would.
 
  • #10
Kpgabriel said:
Right, what did that give you?
92.037. I checked, not the right answer (for part a)
 
  • #11
Brianna I said:
92.037. I checked, not the right answer (for part a)
I am getting a different answer. You have r^2 = (-65.08)^2 + (21.92)^2 ?
 
  • #12
Kpgabriel said:
I am getting a different answer. You have r^2 = (-65.08)^2 + (21.92)^2 ?
Ah, my mistake. I redid it and got 68.67. I just checked and it is correct! Thank you! I will be able to solve for the angle :)
I must have been too sloppy with the numbers, I realized my calculator was still keeping the negative number even while being squared, messing everything up.
Thanks again!
 
  • #13
Brianna I said:
Ah, my mistake. I redid it and got 68.67. I just checked and it is correct! Thank you! I will be able to solve for the angle :)
I must have been too sloppy with the numbers, I realized my calculator was still keeping the negative number even while being squared, messing everything up.
Thanks again!
You're welcome!
 
  • #14
The problem also asks for the direction of the glider's ground track. (In your sketch, the directional sense of vector R is wrong.) It may help to draw the vectors to scale and connect them head to tail to get a preliminary ballpark resultant.
 

1. What is the formula for finding the magnitude of two velocities at an angle?

The formula for finding the magnitude of two velocities at an angle is √(v1² + v2² + 2v1v2cosθ), where v1 and v2 are the two velocities and θ is the angle between them.

2. How do I determine the direction of the resultant velocity?

The direction of the resultant velocity can be determined by using the tan-1(vy/vx) formula, where vy is the vertical component of the velocity and vx is the horizontal component of the velocity. This will give you the angle at which the resultant velocity is directed.

3. Can the magnitude of the resultant velocity be greater than the sum of the individual velocities?

Yes, the magnitude of the resultant velocity can be greater than the sum of the individual velocities if the two velocities are not in the same direction. This is known as vector addition and it follows the rules of vector algebra.

4. What units are used to measure velocity?

Velocity is typically measured in meters per second (m/s) in the SI (International System of Units) system. In some cases, it may also be measured in other units such as miles per hour (mph) or kilometers per hour (km/h).

5. Can the magnitude of the resultant velocity be negative?

Yes, the magnitude of the resultant velocity can be negative if the two velocities are in opposite directions. In this case, the negative sign indicates that the resultant velocity is in the opposite direction of the larger of the two velocities.

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