Person dragging a bow with a rope - Calculate friction

• dois
In summary, the conversation discusses finding the force exerted by a person pulling a box with a mass of 60kg, given that the box is initially moving at 4 m/s and increases to 10 m/s in 3 seconds. The coefficient of friction between the box and the ground is 0.7. The participants also discuss the meaning of coefficient of friction and the equations needed to solve the problem.
dois

Homework Statement

The question says
"A person is dragging a box with the mass of 60kg by a rope. The person begins to drag the box at 4 m/s [F]. All of a sudden the person sees on coming traffic. The person calculates that they have 3 seconds to get out of the way. If at the end of the 3 seconds the box is moving 10 m/s [F] and the coefficient of friction between the box and the ground is 0.7, find the force which the person is pulling the box."

my biggest problem is I don't know what a coefficient is.

Homework Equations

im not to sure what equations i would need to use. My guess would be d=(vi)(t) + 1/2 (a)(t^2)

The Attempt at a Solution

To find out the force which the person is pulling the box would we still use
F= m*a

and we would need to figure out the displacement first with d=(vi)(t) + 1/2 (a)(t^2)

The coefficient of friction, $$\mu$$ is the constant relating the frictional force between two surfaces to the normal contact force between the two surfaces.
$$F_{friction} = \mu N$$​

The velocity of the box increases from 4m/s to 10m/s in 3s. I presume that should be enough for you to obtain the average force exerted on the box during this time period using the standard F=ma?

so μ is 0.7?

yep.

How would we begin this question
my known's are
mass= 60kg
vi=4 m/s [F]
v2=10m/s [F]
t= 10s
friction=0.7

but i don't know what equation to use to find the applied force

you have time, v0 and vf. from there, you must solve for acceleration, then plug it into F = ma , which will be your net force. From there, you must consider all the different forces and single out the pulling force. (Hint: the pulling force is not all that is affecting the pull.. what does friction do?)

dois said:
How would we begin this question
my known's are
mass= 60kg
vi=4 m/s [F]
v2=10m/s [F]
t= 10s
friction=0.7

but i don't know what equation to use to find the applied force

friction is not 0.7, that's the coefficient of friction. Friction is the coefficient of friction multiplied by the normal force

ok, and the normal force is equal to the mass right?
so then it would be
0.7 x 60
which would then be
42?

dois said:
ok, and the normal force is equal to the mass right?
so then it would be
0.7 x 60
which would then be
42?

the normal force is what's keeping the object "up", it is the sum of vertical components.. so in this example, you only have the force of gravity or the weight pushing it down to the ground, so the normal force is equal to the weight

Alright. So then the normal force is 60, because the weight is 60kg.
and then friction would be, 0.7x60=42
is that right?

dois said:
Alright. So then the normal force is 60, because the weight is 60kg.
and then friction would be, 0.7x60=42
is that right?

no, mass and weight are two different things. I think that you should revise your concepts

1. How do you calculate friction in this scenario?

To calculate friction, we first need to determine the coefficient of friction between the bow and the rope, which is a measure of how easily the two surfaces slide against each other. This can be determined through experimentation or by looking up the coefficient for similar materials. Then, we can use the formula F = μN, where F is the frictional force, μ is the coefficient of friction, and N is the normal force (equal to the weight of the bow). This will give us the force required to overcome friction and drag the bow with the rope.

2. What factors affect the amount of friction in this scenario?

The amount of friction in this scenario is primarily affected by the coefficient of friction and the normal force. Other factors that may play a role include the surface roughness of the bow and rope, the tension of the rope, and any external forces acting on the bow (such as wind).

3. How does the angle of the rope affect friction?

The angle of the rope can affect the amount of friction in this scenario. When the rope is pulled at an angle, the normal force decreases, which in turn decreases the frictional force. This means that the bow will be easier to drag with the rope at an angle compared to pulling it straight back.

4. Can friction be completely eliminated in this scenario?

No, it is not possible to completely eliminate friction in this scenario. However, it can be reduced by using materials with lower coefficients of friction, reducing the tension of the rope, and minimizing surface roughness. Friction is a natural force that will always be present to some degree in any situation involving two surfaces in contact.

5. How can the amount of friction be increased in this scenario?

To increase the amount of friction in this scenario, we can use materials with higher coefficients of friction, increase the tension of the rope, or make the surfaces rougher. Additionally, increasing the weight of the bow or pulling the rope at a steeper angle can also increase the frictional force. However, it is important to note that too much friction can cause the rope to break or the bow to become damaged, so it is important to find a balance that allows for efficient dragging without risking damage.

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