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File Edit View History Bookmarks People window Help 98% Fri 9:45 PM a MasteringPhysics: HW 6c Secure 73525940 assignment Winter 2017 Physics 231-02 signed in as Hussein Obad l Help i Cosa POLs1 HW 6C Problem 6.45 Resources k previous l 5 of 5 I return to assignment Problem 6.45 Part A You and your friend Peter are putting new shingles Xcode If the coefficient of kinetic friction between the box and the roof is o.52, with what speed should you on a roof pitched at 25 You're sitting on the very ca top of the roof when Peter, who is at the edge of push the box to have it gently come to rest right at the edge of the roof? the roof directly below you, 5.0 m away, asks you Express your answer to two significant figures and include the appropriate units. for the box of nails. Rather than carry the 2.0 kg box of nails down to Peter, you decide to give the box a push and have it slide down to him A MyPlaygrou ygroun 6.8 Submit My Answers Give Up incorrect; Try Again: 2 attempts remaining Proofde bac Continue

Explanation / Answer

Net force is Fnet = m*g*sin(theta) - F_friction

Work done by the Net force = change in kinetic energy

frictional force is fk = mu_k*m*g*cos(theta)

and let S be the dispalcement of the box before coming to rest

(m*g*sin(theta))-(mu_k*m*g*cos(25))*S = Kf-Ki

since finally the box was coming to rest then Final kinetic energy is Kf = 0.5*m*v^2 = 0.5*m*0^2 = 0 J

initial kinetic energy is ki = 0.5*m*Vo^2

then

-((2*9.8*sin(25))-(mu_k*m*g*cos(theta))_*S = 0-0.5*m*Vo^2

-((2*9.8*sin(25)) - (0.52*2*9.8*cos(25)))*5 = 0.5*2*Vo^2

Vo = 2.18 m/sec

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