Kinetic friction, mass on track when will it stop.

[sg001]

Homework Statement

A block of mass m is initially held in place on the left side of a track at a distance h above the bottom of the track. The track is completely frictionless, with the exception of a rough horizontal section of track of length h which has a coefficient of kinetic friction μ = 0.15. If the block is released from rest, how many times does the block completely cross the rough section of track before it stops?

Homework Equations

The Attempt at a Solution

So I have worked out the height to be 0.85 m, but am stuck on finding an expression for when the ball will stop I have what I think it is

x=number of times without stopping= v^2/2gh

does this see right, and I worked out v = 11.43 but when I plug it in I get 7.84 times... in the answer booklet it says seven but I am not sure if that's because you can't round up because it doesn't make sense so they round down to 7??

 

[emailanmol]

Hey,


I hope this makes it clear enough :-)

how many times does the block completely cross the rough section of track before it stops?

 

[azizlwl]

Wondering how you get the value of h=0.85 m since only a coefficient of kinetic friction μ = 0.15 is given. And not mentioning anything about a ball.

 

[sg001]

Wondering how you get the value of h=0.85 m since only a coefficient of kinetic friction μ = 0.15 is given. And not mentioning anything about a ball.

by the work energy theorem, I worked out how much energy was lost through the distance of friction patch... the height of the track is the same 'height' or distance as the friction patch.

 

[sg001]

Hey,


I hope this makes it clear enough :-)

Yeah thanks, I was assuming that just wanted to check... I did not really pick up on the COMPLETELY part of the question.