Help Solving a Sled Friction Problem

[saralsaigh]

Sled question

I have a physics midterm tonite and i was trying some of the practice tests and i got stuck on this question, ur help would be greatly appreciated :)

1. The problem:
A sled is traveling at 4.00m/s along a horizontal stretch of snow. The coefficeint of kinetic friction is Uk=0.05 and the coefficient of static friction Us=0.07. How far does the sled go before stopping?


2.This is my thought process:
Ok I am assuming its moving at constant speed and the acceleration is negative so i drew the FBD with weight down, normal forced up and force of kinetic friction to the left. (Assuming its moving to the right) i thought that Fnet= force of friction (x-direction) = m a , and that by solving for acceleration i can use it to find out the distance however i don't have mass so I didnt know wat to do?! Any suggestions?


3. The answer is actually 16.3m

 

[neutrino]

Why would you need to know the mass?

 

[denverdoc]

I think if you just follow thru with what you have done already, you are there:

set ma=frictional force and solve for a.

 

[saralsaigh]

well if what i said was correct and fnet(x-direction) = ma = Ff, then
ma = Ukmg right? ohhh ic...lol so a=Ukg... my bad this is where i make another stupid mistake...THANKS