(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

You and your friend Peter are putting new shingles on a roof pitched at 20degrees . You're sitting on the very top of the roof when Peter, who is at the edge of the roof directly below you, 5.4 m away, asks you for the box of nails. Rather than carry the 2.1 kg box of nails down to Peter, you decide to give the box a push and have it slide down to him.

If the coefficient of kinetic friction between the box and the roof is 0.51, with what speed should you push the box to have it gently come to rest right at the edge of the roof?

2. Relevant equations

normal force up y-axis

mg down y-axis

angle left of -y

friction positive x

not 100% sure if these are right

n-mg*cos O=may

fk+mg(sin O)=max

vf=vi+at

xf=xi+vi*t+.5at^2

3. The attempt at a solution

first get normal force which solve for 1st equ.

n=2.1(9.8)cos20=19.34

then find kinetic friction

19.34*.51=9.86

put into next equation

9.86+2.1(9.8)sin20=2.1*a

a=8.047

plug into kinematic equ.

5.4=0+0*t+.5(8.047)t^2

t=1.15

vf=8.047*1.15

vf=9.3

obviously not right cause Im not sure about the free-body diagram any help would be fantastic.

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# Homework Help: Finding the speed with kinetic friction

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