Posted by **Jacob** on Tuesday, October 16, 2012 at 9:46pm.

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 -
**Elena**, Wednesday, October 17, 2012 at 4:43am
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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