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