Is this Free-Body Diagram Correct?

In summary: The F = ma equation tells you the net force on the system, and you can then work out what the acceleration is. Two problems:- you omitted the plus signs, minus signs and parentheses, making it impossible to decipher.- it doesn't apply in your set up; compare the diagramsThe plus signs and minus signs are necessary to solve for the net force. The parentheses are there to show that the force is acting on the system as a whole, not just on the object that is being pulled. Without them, the equation would be incorrect because it would only be calculating the force on the object that is being pulled. The equation applies to the situation in which the object is falling and the force of gravity is acting on
  • #1
DevonR
4
0

Homework Statement


I have to draw a free body diagram representing the motion of an object @ a given point in time. This diagram is for section 1.

It's of a 1.25 kg cart with a 0.6 kg can attached to it with a pulley-system. When the can drops, the cart begins to move. In section one, when the can drops, the cart begins to accelerate forward.

Acceleration = 0.196 m/s(squared)
Mass of cart = 1.25 kg
Mass of can = 0.6 kg

Homework Equations

F = ma

The Attempt at a Solution



The diagram is uploaded here. I just want to know if this seems to be correct?

EDIT:

Heres the assmuptions I made

I calculated net force w/ acceleration provided = 0.196 m/s
and with the total mass (1.25 kg + 0.6 kg) = 1.9 kg
Net force = 0.37 N

I did normal force & force of gravity on the cart, which was 12.3 N for both.
The falling can was what caused the motion of the cart, so I calculated Fg = 5.9 N for the 0.6 kg can. No normal force obviously because it wasn't sitting on a surface.

But the can was attached to a string, which slowed down the falling can's motion. So I had to calculate F-tension. I used this formula to calculate it;

Force of Tension = 2m1m2/m1m2 x Gravity

I got 4N (3.97N) as the tension force.

So I assumed that the applied force would be Force of Gravity on the can MINUS the Force of Tension of the string holding the can. The applied force was 1.9 N

Then I calculated force of friction.
I assumed it to be the applied force minus net force
Which was 1.9 N - 0.37 N

For friction I got 1.5 N.

Does all of this seem correct? [/B]


freebody.jpg
 

Attachments

  • freebody.jpg
    freebody.jpg
    24.3 KB · Views: 441
Last edited:
Physics news on Phys.org
  • #2
I would have thought the set up would be so that the falling can moves the cart horizontally. As you've drawn it, the force on the cart is vertical.
 
  • #3
Thanks for the reply! I added a written description of my 'attempt @ a solution' to the original post.
I see what you mean, so I should draw Fa = 1.9 horizontally.

Aside from that, is everything else okay?
 
  • #4
DevonR said:
I got 4N (3.97N) as the tension force.
How did you get that? Without the tension, the acceleration would be g. So what tension is required to reduce it to the given acceleration?
 
  • #5
haruspex said:
How did you get that? Without the tension, the acceleration would be g. So what tension is required to reduce it to the given acceleration?

I used this formula Force of Tension = 2m1m2/m1m2 x Gravity
to get the force of tension


 
  • #6
DevonR said:
I used this formula Force of Tension = 2m1m2/m1m2 x Gravity
to get the force of tension

I've no idea where you get that equation from. All the m's seem to cancel.
 
  • #8
DevonR said:
I got the formula from here

http://www.citycollegiate.com/tension1.htm
Two problems:
- you omitted the plus signs, minus signs and parentheses, making it impossible to decipher.
- it doesn't apply in your set up; compare the diagrams
It's quite easy from first principles without searching for answers on the net. Just consider the FBD of the hanging mass.
 

What is a free-body diagram?

A free-body diagram is a simplified representation of an object or system showing all the external forces acting on it. It is often used in physics and engineering to analyze the motion and interactions of objects.

Why is it important to check if a free-body diagram is correct?

It is important to check if a free-body diagram is correct because it ensures that all the forces acting on the object are accurately represented. By doing so, we can accurately analyze the motion and predict the behavior of the object.

What are the common mistakes made in creating a free-body diagram?

Some common mistakes in creating a free-body diagram include forgetting to include all the external forces, labeling forces incorrectly, and drawing the forces at incorrect angles or positions. It is important to double check your diagram to avoid these mistakes.

How can I tell if a free-body diagram is correct?

A correct free-body diagram should have all the external forces labeled and drawn in the correct direction and magnitude. The forces should also be balanced, meaning that the sum of all the forces in any direction is equal to zero.

Are there any resources available to help me check the correctness of a free-body diagram?

Yes, there are various online resources and textbooks that provide step-by-step guides and examples on how to create and check free-body diagrams. Additionally, you can seek help from a teacher or tutor to ensure the accuracy of your diagram.

Similar threads

  • Introductory Physics Homework Help
Replies
5
Views
466
  • Introductory Physics Homework Help
Replies
12
Views
628
  • Introductory Physics Homework Help
Replies
4
Views
1K
  • Introductory Physics Homework Help
Replies
9
Views
808
  • Introductory Physics Homework Help
Replies
14
Views
2K
  • Introductory Physics Homework Help
Replies
9
Views
4K
  • Introductory Physics Homework Help
Replies
10
Views
2K
Replies
44
Views
1K
  • Introductory Physics Homework Help
Replies
2
Views
1K
  • Introductory Physics Homework Help
Replies
13
Views
537
Back
Top