# Frictional Forces

by Confused too
Tags: forces, frictional
 P: 6 1. The problem statement, all variables and given/known data A baseball player slides into third base with an initial speed of 7.9 m/s. If the coefficient of kinetic friction the player and the ground id .41, how far does the player slide before coming to rest 2. Relevant equations vf^2=vi^2 + 2ad kf=μm 3. The attempt at a solution I tried subsituting but I need acceleration and distance. I didn't know where to go from there
 P: 52 Are you given mass of the baseball player?
P: 6
 Quote by Ace. By kf=μm do you mean Fk = μk x FN? Note that FN is the normal force which in this case is equal to force of gravity. This equation may also be of use to you : a = FUN / m
sorry, yeh you're right with the formula

but why is the normal force equal to gravity and what is FUN

 P: 52 Frictional Forces Sorry, do you have mass?
 P: 6 No, no mass is given
Mentor
P: 41,563
 Quote by Confused too I tried subsituting but I need acceleration and distance.
Use Newton's 2nd law to find the acceleration. The only force acting (at least horizontally) is friction.

Just call the mass 'm'. You won't need an actual value.
P: 6
 Quote by Doc Al Use Newton's 2nd law to find the acceleration. The only force acting (at least horizontally) is friction. Just call the mass 'm'. You won't need an actual value.
I don't understand. F=ma so a=F/m but we don't have an F. I don't really understand frictional forces at all
HW Helper
Thanks
P: 26,148
Hi Confused too! Welcome to PF!
 Quote by Confused too A baseball player slides into third base with an initial speed of 7.9 m/s. If the coefficient of kinetic friction the player and the ground id .41, how far does the player slide before coming to rest
 Quote by Confused too I don't really understand frictional forces at all
You have the coefficient of frictionk = 0.41) …
so if the mass is m, what is the friction force?
(btw, you can then use the work energy theorem)
P: 6
 Quote by tiny-tim Hi Confused too! Welcome to PF!
thanks

 You have the coefficient of friction (µk = 0.41) … so if the mass is m, what is the friction force? (btw, you can then use the work energy theorem)
But we're not given m and what's the work energy theorem?
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