# Work and work of friction

• gcharles_42
In summary, a 45 kg box at rest on a flat floor has a coefficient of kinetic friction of 0.60. A woman applies a horizontal force of 539 N until the box reaches a speed of 2 m/s. The CM-work done by the friction force on the box and the work done by the woman on the box can be solved by drawing a free body diagram and considering the multiple forces at work in the problem.

## Homework Statement

A box of mass 45 kg is initially at rest on a flat floor. The coefficient of kinetic friction between the box and the floor is 0.60. A woman pushes horizontally against the box with a force of 539 N until the box attains a speed of 2 m/s.

What is the CM-work done by the friction force on the box?

What is the work done by the woman on the box?

W= F (Δ x)

## The Attempt at a Solution

I tried solving for delta x by using force and mass to calculate for acceleration and then acceleration, Vo and Vf to find d (which I thought was Δ x) with the equation vf^2 = vo^2 + 2(a) d but I got the wrong answer

gcharles_42 said:

## Homework Statement

A box of mass 45 kg is initially at rest on a flat floor. The coefficient of kinetic friction between the box and the floor is 0.60. A woman pushes horizontally against the box with a force of 539 N until the box attains a speed of 2 m/s.

What is the CM-work done by the friction force on the box?

What is the work done by the woman on the box?

W= F (Δ x)

## The Attempt at a Solution

I tried solving for delta x by using force and mass to calculate for acceleration and then acceleration, Vo and Vf to find d (which I thought was Δ x) with the equation vf^2 = vo^2 + 2(a) d but I got the wrong answer

You should get in the habit of drawing a free body diagram. They can basically solve the entire problem for you most of the time.

If you do that, you will notice there are multiple forces at work here!

Zondrina said:
You should get in the habit of drawing a free body diagram. They can basically solve the entire problem for you most of the time.

If you do that, you will notice there are multiple forces at work here!

This. Free body diagrams are the best thing that ever happened to intro mechanics.

Always show your work so we can tell you where it went wrong.