Question about coefficient of kinetic friction and distance

In summary: This is incorrect - you need to use the m (the mass of the block) in order to find F. In summary, a block pushed against a spring with a constant compression force causes the spring to stretch by an amount K.
  • #1
RayanLhindi
2
0
Question.png


1. Homework Statement

m = 4.00 kg
theta = 30
v = 1 m/s
compression of the spring by the block , x = 0.3 m
d = 5 m

Homework Equations



rule : Fk = μ k * N
i must find Fk first to find μ k using conservation energy,
[/B]

The Attempt at a Solution


First find N,
N = m x g x cos theta
N = 4 * 9.81 * cos30 = 33.98N
then we find the force to find the spring constant
F = ma
F = 4 * 9.81 = 39.24N
KE = 0.5 mv^2
KE = 0.5 * 39.24 * 1^2 = 19.62J
PE = 0.5 kx^2 => 0.5 Fx
PE = KE
0.5 Fx = 0.5 mv^2
x = v^2 / a = 1^2 / 9.81 = 0.101m
K = f/x = 392.4
-------------------------
Here i am confused, our professor told us to use mechanical energy and conservation energy to find Fk ,
and the rules is
delta E = delta E mechanics + delta E thermo + delta E internal
K2 + U2 = K1 + U1 The question is long and very tricky, i solve what i can, and i not sure about it actually, if you can help me i will be very thankful.
 
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  • #2
You don't appear to have used the data from the first part of the experiment - on the horizontal frictionless surface. The purpose of the first part is to allow you to calculate the spring constant using conservation of energy techniques. You can then use the spring constant to solve the second part on the frictional, inclined surface.

PS: The spring constant K that you calculate above is not correct. It's much easier to calculate it using the horizontal info - and hence less likely to generate errors.
 
  • #3
andrewkirk said:
You don't appear to have used the data from the first part of the experiment - on the horizontal frictionless surface. The purpose of the first part is to allow you to calculate the spring constant using conservation of energy techniques. You can then use the spring constant to solve the second part on the frictional, inclined surface.

PS: The spring constant K that you calculate above is not correct. It's much easier to calculate it using the horizontal info - and hence less likely to generate errors.

I will check the spring constant again no problem, but the first part how to solve it ? Can you give me a hint ? Cuz I am so confused now if all this calculations is for nothing :(
 
  • #4
To solve for the spring constant write an equation that equates the block's KE from the horizontal case, when not in contact with the spring the spring, with the PE of spring compression at maximum compression. One of those two amounts involves K and all other quantities in the two amounts are known, so you can solve for K.
 
  • #5
RayanLhindi said:
F = ma
F = 4 * 9.81 = 39.24N
KE = 0.5 mv^2
KE = 0.5 * 39.24 * 1^2 = 19.62J
You calculated a force, F (what force do you think this is?) then appear to have used the resulting number as though it is a mass.
 

1. What is the coefficient of kinetic friction?

The coefficient of kinetic friction is a constant value that represents the amount of friction between two surfaces in motion. It is denoted by the symbol μ and has no units.

2. How is the coefficient of kinetic friction calculated?

The coefficient of kinetic friction can be calculated by dividing the force of friction by the normal force. This can be represented by the equation μ = Fk/N, where Fk is the force of kinetic friction and N is the normal force.

3. What factors affect the coefficient of kinetic friction?

The coefficient of kinetic friction is affected by the types of surfaces in contact, the roughness of the surfaces, and the presence of any lubricants. It also varies with the speed of the objects in motion.

4. How does the coefficient of kinetic friction affect distance traveled?

The coefficient of kinetic friction plays a role in determining the amount of work required to move an object over a distance. The higher the coefficient of kinetic friction, the more work is needed and the shorter the distance traveled by the object.

5. Can the coefficient of kinetic friction be greater than 1?

Yes, the coefficient of kinetic friction can be greater than 1. This indicates a very high amount of friction between two surfaces, making it difficult for an object to move.

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