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# Use coeff of kin. friction, and initial velocity, to work out distance? watch

1. I have a question involving something sliding across a horizontal surface.
The kinetic friction has coeff. of mew(k)

Initial velocity is v0, and I have to calculate the distance travelled when final velocity (v) = 0ms-1.

To calculate the distance, I used suvat and was wrong, so I assume acceleration (deceleration in this case) is not constant.

I have made a free-body diagram, and sum of Fy = normal force - weight = 0
Sum of Fy = kinetic friction force - ma (not sure what that force is called..) = 0.

Then, using Kinetic friction = mew(k)*normal = mew(k)*mg = ma, I cancelled the masses out, to get mew(k)*g = a.

I have no idea why, but I equated kinetic energy = kinetic friction = ma.

Anyway, do I now use v^2 = v(o)^2 + 2as to get the distance, s?
2. (Original post by PhysicsGal)
I have a question involving something sliding across a horizontal surface.
The kinetic friction has coeff. of mew(k)

Initial velocity is v0, and I have to calculate the distance travelled when final velocity (v) = 0ms-1.

To calculate the distance, I used suvat and was wrong, so I assume acceleration (deceleration in this case) is not constant.

I have made a free-body diagram, and sum of Fy = normal force - weight = 0
Sum of Fy = kinetic friction force - ma (not sure what that force is called..) = 0.

Then, using Kinetic friction = mew(k)*normal = mew(k)*mg = ma, I cancelled the masses out, to get mew(k)*g = a.

I have no idea why, but I equated kinetic energy = kinetic friction = ma.

Anyway, do I now use v^2 = v(o)^2 + 2as to get the distance, s?
The initial kinetic energy goes completely into work done against friction as the final speed is 0. i.e. initial kinetic energy = work done against friction

Given that work done against friction is F*x where F is the frictional force and x is distance travelled, can you see where to go?
3. (Original post by Dark Lord of Mordor)
The initial kinetic energy goes completely into work done against friction as the final speed is 0. i.e. initial kinetic energy = work done against friction

Given that work done against friction is F*x where F is the frictional force and x is distance travelled, can you see where to go?
Right, thank you Solved it

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