here is the question and answer in the small box i used law of conservation of e

Question

here is the question and answer in the small box

i used law of conservation of energy which is

with work = 0, KEo =0 and PEf =0

=>

i dont know where did i do wrong

b/ i dont know how to solve it

here is the question and answer in the small box DeltaE/Fn = 13.72 / (2*9.8) = 0.7 i dont know where did i do wrong b/ i dont know how to solve it DeltaE is basiclly just the friction force so i use the formular uk = DeltaE = 13.72N and DeltaE = mgh - 1/2 mv2 =>DeltaE DeltaE with work = 0, KEo =0 and PEf =0 => mgh = 1/2 mv2 + i used law of conservation of energy which is W + PEo + KEo= PEf + KEf +

Explanation / Answer

Wf = -f*s = -u*m*g*s

Eb + Wf = Ec

0.5*m*vb^2 - u*m*g*s = 0

u = vb^2/(2*g*s) = (4.2*4.2)/(2*9.8*3) = 0.3

b) Ea + Wf = Eb

m*g*R + Wf = 0.5*m*vb^2

Wf = 0.5*m*vb^2 - m*g*R

Wf = m*(0.5*vb^2 - gR)

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