2 Questions - Fnet with a Vector + Forces

In summary, Harry and Ashley were pulling a sled. Harry pulled at 15 degrees West of South at 400N and Ashley pulled at 50 degrees North of West at 375N. They encountered friction to the east at 150N. The overall force (Fnet) on the sled, using a scaled vector drawing, was 38.46N.
  • #1
:confused: :confused: :confused:

First question

Harry and Ashley were pulling a sled. Harry pulled at 15 degrees West of South at 400N and Ashley pulled at 50 degrees North of West at 375N. They encountered friction to the east at 150N. Calculate the overall force (Fnet) on the sled, using a scaled vector drawing. Use a scale of 50N to 1 cm.

I have the drawing finished, but I don't know how to figure out Fnet? I am really confused...

Second Question

A rightward force is applied to a 10-kg object to move it across a rough surface at constant velocity. The coefficient of friction, µ, between the object and the surface is 0.2. Draw a free body diagram to determine the graviational force, normal force, applied force, frictional force, and net force. Neglect air resistance.

For this one, I have the diagram, basically a square with an arrow from each Side

Upwards is Fnorm, Right is Fapp, Downwards is Fgrav, and Left is Ffric.

I have no idea how to do this one either. I'd appreciate some help, thanks. :redface:
 
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  • #2
For your first question, the easiest solution is to break all the forces up into there x and y components and then solve them this way

for example, the force that Harry exerts could be broken into
[tex]F_{x}= -400N sin(15)[/tex]
[tex]F_{y}= -400N cos(15)[/tex]
Once you do this for all the forces you can add them up easily (it may be easier to draw the forces again once you have broken them up)

For your second question it takes more thought and less calculation
Think about how the Normal force relates to the gravitational force
Also think about the relationship between the frictional force, and the force being exerted on the object

If that still does not make it clear, think about a block on a table. What happens when you push it. What does that tell you about the net force acting on it. Remember that you diagram must represent what actual happens in the physical case.
 
  • #3
Marthius said:
For your first question, the easiest solution is to break all the forces up into there x and y components and then solve them this way

for example, the force that Harry exerts could be broken into
[tex]F_{x}= -400N sin(15)[/tex]
[tex]F_{y}= -400N cos(15)[/tex]
Once you do this for all the forces you can add them up easily (it may be easier to draw the forces again once you have broken them up)

For your second question it takes more thought and less calculation
Think about how the Normal force relates to the gravitational force
Also think about the relationship between the frictional force, and the force being exerted on the object

If that still does not make it clear, think about a block on a table. What happens when you push it. What does that tell you about the net force acting on it. Remember that you diagram must represent what actual happens in the physical case.

Sorry, but I still do not understand. We haven't used sin or cos in any of our equations yet so I do not see how I use that..?

And for your explanation on my second question, I don't understand that either sorry.

This class is basically an introductory course for people who have never ever taken physics before, so you guys will have to explain how to do the questions to me in laymans terms. :P

edit:

I figured out the first question, I think... following your help. I got 38.46 after adding up both the Fx and Fy numbers for Harry and Ashley then subtracting them. Thanks!
 
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1. What is Fnet and how is it related to vectors and forces?

Fnet, also known as net force, is the overall force acting on an object. It is calculated by adding all of the individual forces acting on the object, taking into account their direction and magnitude. This is where vectors come into play, as they represent both the direction and magnitude of a force. Therefore, Fnet is a vector quantity.

2. How do you calculate Fnet when multiple forces are acting on an object?

To calculate Fnet, you need to add all of the individual forces acting on the object together. This can be done using vector addition, where you add the x-components of the forces together and then the y-components together. The resulting x and y components can then be combined to find the magnitude and direction of Fnet.

3. Can Fnet be negative?

Yes, Fnet can be negative. This occurs when the forces acting on an object are in opposite directions, canceling each other out. In this case, the net force is in the direction of the larger force, but will have a negative value.

4. How does the direction of Fnet affect an object's motion?

The direction of Fnet determines the direction of an object's motion. If Fnet is in the same direction as an object's initial velocity, the object will continue to move in that direction. If Fnet is in the opposite direction, the object will slow down and eventually come to a stop. If Fnet is perpendicular to the object's initial velocity, it will cause the object to change direction.

5. What happens to an object if the net force acting on it is zero?

If the net force on an object is zero, the object will either remain at rest or continue moving at a constant velocity. This is known as Newton's first law of motion, which states that an object will remain at rest or in motion with a constant velocity unless acted upon by a net force.

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