# physics

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A block is released from rest at the top of an incline which makes a 30 degree angle with the horizontal. The incline is 12 m long and it takes the block 25 seconds to reach the bottom. What is the coefficient of kinetic friction, between the block and the incline?

• physics -

s=at²/2
a=2s/t²=2•12/25²=0.0384 m/s²
v=at=0.0384•25=0.96 m/s

PE=KE+W(fr)

PE=m•g•h=m•g•s•sinα,
KE=mv²/2,
W(fr) =μ•m•g•cosα•s,
m•g•s•sinα= mv²/2+ μ•m•g•cosα•s,

μ ={2g•s•sinα - v²}/2•g•cosα•s=
=tanα - v²/2•g•s •cosα

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