# Finding the kinetic friction between the block and surface

• gijungkim
In summary, the conversation is about finding the coefficient of kinetic friction between a block and a horizontal surface. The block is pulled at a constant speed by a force of 14 N at an angle of 35°. The equations used to solve the problem are Fx = Fcos(theta), Ff = Fn * Uk, F=ma, and Fn = mg. The person asking the question initially got a value of 0.234 for the coefficient of kinetic friction but later realized they forgot to include Fsin(theta). The correct answer is 0.28.
gijungkim

## Homework Statement

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The block shown is pulled across the horizontal surface at a constant speed by the force shown. If M = 5.0 kg, F = 14 N and Theta= 35°, what is the coefficient of kinetic friction between the block and the horizontal surface?

## Homework Equations

Fx = Fcos(theta)
Ff = Fn * Uk (Friction equation)
F=ma
Fn = mg

## The Attempt at a Solution

I did it by myself and got 0.234, but the answer says it's 0.28. Can you explain this to me?

My work:
a = F / m
a =( Fcos(35) - Fn * Uk ) / m= 0
Fcos(35) / Fn = Uk
14*cos(35) / (5 * 9.8) = 0.234 = Uk

I don't know where I did wrong

#### Attachments

• image.jpg
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Nevermind! I got it! I forgot the Fsin(theta)
It is
Fcos(theta) - Uk(mg - Fsin(theta)) = 0
14 * cos(35) / (5*9.8 - 14 sin(35)) = 0.28 = Uk

## What is kinetic friction?

Kinetic friction is the force that opposes the motion of an object when it is in contact with a surface and moving.

## How is kinetic friction different from static friction?

Kinetic friction is the force that acts between two surfaces in contact when they are in motion, while static friction is the force that prevents an object from moving when it is at rest.

## What factors affect the magnitude of kinetic friction?

The magnitude of kinetic friction is affected by the nature of the surfaces in contact, the force applied to the object, and the roughness of the surfaces.

## How can I determine the kinetic friction between a block and a surface?

To determine the kinetic friction between a block and a surface, you can use the formula Fk = μkN, where Fk is the force of kinetic friction, μk is the coefficient of kinetic friction, and N is the normal force exerted by the surface on the object.

## Why is finding the kinetic friction important?

Finding the kinetic friction is important because it helps us understand and predict the motion of objects on surfaces. It also allows us to calculate the amount of force needed to overcome the friction and keep an object in motion.

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