This was on my exam. I wasn't sure how to solve it.

  • Thread starter PhysicsKid0123
  • Start date
  • Tags
    Exam
In summary, the student is seeking help with solving for force vectors and the angle between force and displacement. The force and displacement are in the same direction and the particle is starting from rest. The formula used to calculate this is W = Frcosθ. The magnitude of the force can be found using this equation and a unit vector can also be determined in the same direction as the force and displacement.
  • #1
PhysicsKid0123
95
1

Homework Statement


I tried to solve for the force vectors but I had no clue how to do it? I tried plenty of times after the exam and still haven't found the components. Help?

Homework Equations



F[itex]\bullet[/itex][itex]\Delta[/itex]r

The Attempt at a Solution

 

Attachments

  • photo (8).jpg
    photo (8).jpg
    27.6 KB · Views: 454
Physics news on Phys.org
  • #2
Can you express ##\vec{F} \cdot \Delta\vec{r}## in terms of the magnitude of the force, the magnitude of the displacement, and the angle between the force and the displacement?

In this problem, what is the angle between the force and the displacement?
 
Last edited:
  • #3
Yes, but I don't see how you can find the angle between them. You need a given angle or the force vector?
 
  • #4
The particle starts from rest. The force is constant in magnitude and direction. So, how does the direction of the force relate to the direction of the displacement?
 
  • #5
They relate by the dot product of the force vector and position vector. Vector F dot Vector r = abs F * cos()* abs r. Or by components, vector F dot vector r = Fx*rx + Fy*ry...
 
  • #6
OK. So ##W = Frcosθ##.

You should be able to get the magnitude of the force from this equation. You just need to know what to use for r and θ.
Once you get ##F## you should be able to express the force vector ##\vec{F}## in component form.
 
  • #7
When you push something at rest, what direction does it move with respect to the force you applied?
 
  • #8
I don't see how you can find the angle to begin with.. For r I'd simply use sqrt(20).
 
  • #9
If an object is at rest when a force is applied in the x direction, which way does the object move?
 
Last edited:
  • #10
According to the problem statement, the force and displacement are going to be pointing in the same direction. So the angle between them is zero. First calculate the magnitude of the force necessary to cause 24 J of work when the particle travels sqrt(20) meters. Then determine the equation for a unit vector in the same direction as r. This will be the unit vector in the direction as F also.

Chet
 

Related to This was on my exam. I wasn't sure how to solve it.

1. How do I approach a problem that I am unsure how to solve on an exam?

When faced with a problem that you are unsure how to solve on an exam, it is important to stay calm and focused. Start by carefully reading and understanding the question, and then break it down into smaller, more manageable parts. Use any formulas, equations, or concepts that you have learned to guide your thinking and approach the problem step by step. If you are still unsure, try to eliminate any obviously incorrect options and make an educated guess.

2. Should I skip a problem that I am unsure about and come back to it later?

It depends on the structure of the exam and your individual test-taking strategy. Some students prefer to skip a problem and come back to it later, while others prefer to tackle the difficult questions first. If you do decide to skip a problem, make sure to leave enough time at the end to revisit it and give it your best shot.

3. How can I prepare for these types of problems before an exam?

The best way to prepare for problems that you are unsure about is to practice. Make sure to review your notes and class materials regularly, and attempt practice problems or past exam questions. This will not only help you become more familiar with the material but also give you a better understanding of how to approach and solve different types of problems.

4. What should I do if I run out of time and can't solve a problem on the exam?

If you find yourself running out of time and unable to solve a problem, it's important to not panic. Take a deep breath and try to make an educated guess based on any information you do know. Remember, partial credit is often given for showing your thought process and attempting the problem, so try to write down any relevant equations or concepts you can remember.

5. Is it okay to ask for help if I am unsure how to solve a problem during the exam?

It depends on the rules set by your instructor. Some exams may allow for clarification or assistance, while others may not. If you are unsure, it's always best to ask your instructor beforehand. During the exam, if you are allowed to ask for help, make sure to phrase your question carefully and avoid giving away any potential answers to other students. It's also important to note that asking for help should be a last resort and you should try to solve the problem on your own first.

Similar threads

  • Introductory Physics Homework Help
Replies
10
Views
310
  • Introductory Physics Homework Help
Replies
7
Views
1K
Replies
4
Views
1K
  • Introductory Physics Homework Help
Replies
10
Views
1K
  • Introductory Physics Homework Help
Replies
2
Views
1K
  • Introductory Physics Homework Help
Replies
1
Views
1K
Replies
2
Views
2K
  • Introductory Physics Homework Help
Replies
10
Views
2K
  • Introductory Physics Homework Help
Replies
6
Views
1K
  • Introductory Physics Homework Help
Replies
3
Views
1K
Back
Top