# Internal Energy and kinetic friction

• hats_06
In summary, the question is asking for the increase in internal energy of a block being dragged over a rough surface. The formula for change in internal energy is equal to the work done against friction. To solve, first find the normal force by analyzing all vertical forces acting on the block. Then use the formula for friction (Ff = ukN) and the given values to find the work done against friction. The final answer should be 27.3 J.

## Homework Statement

Please help, I've been struggling with this question for so long! We haven't done internal energy so I am not sure even where to really begin?

A 10.0 kg block is dragged over a rough, horizontal surface by a 76.0 N force acting at 20.0° above the horizontal. The block is displaced 3.50 m, and the coefficient of kinetic friction is 0.300.

What is increase in internal energy of the block-surface system due to friction?

The change in internal energy equals the work done against friction.

so if Ff= Uk.N...Then since Uk = 0.3 and N = 76.sin 20
So Ff = 7.8, Hence W = 7.8 x 3.5 = 27.3? I tried that answer but it didnt work :S

hats_06 said:
so if Ff= Uk.N...Then since Uk = 0.3 and N = 76.sin 20
First you must correctly solve for the normal force. 76sin20 is the vertical component of the applied force, not the normal force.

To find the normal force, analyze all the vertical forces that act on the block. Since the block doesn't accelerate vertically, vertical forces must sum to zero. Hint: There are three forces acting on the block that have vertical components; the normal force is one of them.

## 1. What is internal energy?

Internal energy refers to the total energy stored in a system, including both its potential and kinetic energy. It is the sum of the microscopic energy of the particles within the system.

## 2. How does internal energy affect temperature?

Internal energy is directly related to the temperature of a system. As the internal energy increases, so does the temperature, and vice versa. This is because an increase in internal energy means the particles within the system are moving faster, which raises the temperature.

## 3. What is kinetic friction?

Kinetic friction is the force that opposes the motion of an object as it slides over a surface. It is caused by the microscopic irregularities between the two surfaces that come into contact with each other.

## 4. How does kinetic friction affect the movement of an object?

Kinetic friction acts in the opposite direction of an object's motion, slowing it down and eventually bringing it to a stop. The amount of kinetic friction depends on the types of surfaces in contact, the force pressing the surfaces together, and the speed of the object.

## 5. Can kinetic friction be reduced?

Yes, there are ways to reduce the amount of kinetic friction between two surfaces. One way is to use a lubricant, such as oil or grease, to create a smoother surface between the two objects. Another way is to reduce the force pressing the objects together or to use materials with lower coefficients of friction.