# Coeffiecent of Kinetic Friction Problem

• c.melissas
In summary: The acceleration is equal to the negative of the coefficient of kinetic friction times the acceleration due to gravity.In summary, the car was traveling at 15 meters/second on a horizontal road and came to a stop in 4 seconds when the brakes were applied. The coefficient of kinetic friction between the tires and the road was used to calculate the time it took for the car to stop, which was approximately 0.38 seconds. The equation used was v = at, where v is the velocity, a is the acceleration, and t is the time. By solving for acceleration and applying Newton's 2nd law, the force of friction was determined to be the force slowing the car down to a stop. The mass of the car was not
c.melissas
1. A car is traveling at 15 meters/second on a horizontal road. The brakes are applied and the car sids to a stop in 4 seconds. The coefficient of kinetic friction between the tires and the road is

2. Coefficient of kinetic friction = friction / Normal Force

3. Time to stop / Velocity = 4/15 = .2666. The correct answer is roughly .38, but I have no idea on how to arrive at that.

c.melissas said:
1. A car is traveling at 15 meters/second on a horizontal road. The brakes are applied and the car sids to a stop in 4 seconds. The coefficient of kinetic friction between the tires and the road is

2. Coefficient of kinetic friction = friction / Normal Force

3. Time to stop / Velocity = 4/15 = .2666. The correct answer is roughly .38, but I have no idea on how to arrive at that.
Where does this equation come from? v = at. Solve for a, then apply Newton's 2nd law to the car.

Thanks for the help. I really had no idea how to answer this problem. I am confused on what do after solving for acceleration because I could not find a way to determine the force or the mass of the car.

You may not need to know the mass, write out Newton's 2nd for the car. The force acting on the car is the friction force, which is slowing it down (decelerating it) to a stop.
And by the way,welcome to PF!

Last edited:
Thank you, and I was able to figure it out.

## What is the coefficient of kinetic friction?

The coefficient of kinetic friction is a measure of the amount of friction between two surfaces in motion. It is represented by the symbol μk and is a unitless value.

## How is the coefficient of kinetic friction calculated?

The coefficient of kinetic friction is calculated by dividing the force of kinetic friction by the normal force between the two surfaces. It can also be determined experimentally by measuring the force required to keep an object in motion at a constant speed.

## What factors affect the coefficient of kinetic friction?

The coefficient of kinetic friction is influenced by several factors, including the nature of the surfaces in contact, the roughness of the surfaces, and the presence of any lubricants or contaminants.

## How does the coefficient of kinetic friction differ from the coefficient of static friction?

The coefficient of kinetic friction measures the amount of friction between two surfaces in motion, while the coefficient of static friction measures the amount of friction between two surfaces at rest. The coefficient of static friction is typically higher than the coefficient of kinetic friction.

## Why is the coefficient of kinetic friction important?

The coefficient of kinetic friction is important because it can help predict the behavior of objects in motion, such as the amount of force required to keep an object moving at a constant speed. It is also useful in engineering and design to determine the best materials and surfaces for reducing friction.

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