What are the forces involved in a brake test on dry concrete?

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In summary, the conversation discusses a problem involving a Porsche Boxter performing a brake test on dry concrete. The initial speed, stopping distance, and mass of the car are given, and the question asks for the average acceleration and stopping friction force during non-skidding braking. The conversation also mentions attempting to solve for the stopping distance during skidding on dry concrete, but getting stuck due to the large magnitude of the results. The solution suggests using the coefficient of kinetic friction to calculate the force in this scenario.
  • #1
Mike12345
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So I am stuck on another question I've been looking at

Ina brake test on dry concrete a Porsche Boxter traveling with an initial speed of 33.2 m/s can stop w/o skidding after moving 62.8 m . The mass of the Boxter including driver is 1340kg.

Determine the magnitude of the average accelertaion of the car during the non skidding braking

a = 87.76 m/s^2 <- i got this which i believe is correct

b) Cacluate the magnitude of the average stopping friction force

Ff ? Stuck here

c) Assume the test is now done with skidding on dry concrete. Calculate the stopping distance during the skid

Fk = 10,505,6 N
A = Fk/m = 7.84 m/s^2

Im stuck here too =S
 
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  • #2
a = 87.76 m/s^2 <- i got this which i believe is correct
This is way too large (driver will not survive). Better run it through again!

average stopping friction force
Friction force is the ONLY force acting on the car (horizontally). So use F=ma to find the total force on the car and you've got it.

skidding on dry concrete
The only difference here is that the car is slipping so you use the coefficient of kinetic friction instead of static friction. You must have a table of these coefficients so you can look it up. Then use the coefficient in the friction formula to calculate the force.
 

1. What is the difference between mass and weight in the context of forces?

Mass refers to the amount of matter an object contains, while weight is the force exerted on an object by gravity. In other words, mass is a physical property that does not change, whereas weight can vary depending on the strength of gravity.

2. How do you calculate net force?

Net force is calculated by adding up all the individual forces acting on an object. This can be done by using vector addition, where forces in the same direction are added and forces in opposite directions are subtracted.

3. What is the difference between balanced and unbalanced forces?

Balanced forces are equal in magnitude and opposite in direction, resulting in a net force of zero. Unbalanced forces, on the other hand, have a net force that is not equal to zero, causing an object to accelerate in the direction of the net force.

4. How does Newton's Second Law of Motion relate to forces?

Newton's Second Law of Motion states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. This means that the greater the force applied, the greater the acceleration will be, and the greater the mass of the object, the less acceleration there will be for a given force.

5. Can forces act on non-physical objects?

No, forces can only act on physical objects with mass. Non-physical objects, such as thoughts or emotions, do not have mass and therefore cannot experience forces.

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