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## Homework Statement

A box of unknown mass slides across a frictionless floor with an initial speed of 4.7 m/s. It encounters a rough region where the coefficient of friction is µk = 0.3

Part 1:

What is the shortest length of rough floor which will stop the box?

Part 2:

What is the shortest length of rough floor which will stop the box?

## Homework Equations

vf^2 = vi^2 + 2a delta x.

Frictional force = mew times the normal force

## The Attempt at a Solution

Final velocity = 0, so

0 = 4.7 ^2 + 2A delta x.

A = the frictional force.

How can I determine the normal force (and after that, the frictional force, and after that, the change in distance) if I don't know the weight of the box? Is there another way to do this problem?