# Finding the coefficient of friction

## Homework Statement

A 100 kg bale of hay falls off a truck traveling along a level road at 24.4 m/s. It lands flat on the road and slides 100m before coming to rest. Assume the acceleration is constant, compute the coefficeient of kinetic friction between the road and the hay.

## Homework Equations

F=u x N
Sum of the forces horizontally (x) = 2440 N -f = ma (acceleration is a constant)
Sum of the forces Vertically (y) = N-W=O

## The Attempt at a Solution

f= (2440)/(100a)
W= -980 so N= -980
now i plugged into f= u x N
(2440/100a)= u x -980
u= -.02a

Now i know the answer because i can see it in the back of the book, and this doesnt feel right. advice?

## Answers and Replies

gneill
Mentor
Now i know the answer because i can see it in the back of the book, and this doesnt feel right. advice?
Don't look in the back of the book? Can you explain where your numbers come from? What's 2440N? It would appear to have the same digits as the initial velocity but I don't see a calculation behind it.

i made the initial velocity into a force. 24.4 m/s x 100kg =2440 N

NascentOxygen
Staff Emeritus
Science Advisor
When you get an answer that looks like the calibre of a bullet, you're probably right.

gneill
Mentor
i made the initial velocity into a force. 24.4 m/s x 100kg =2440 N

Velocity is not force. Mass x Velocity is momentum, not force. They are quite different things.

Hint: Find the acceleration given the provided information. Then use Newton's second law to find the force that acted to produce that acceleration.

thank you so much! that made things so much easier for me <3