For the skier to come to rest, it has to lose all its kinetic energy. Ignoring the drag force caused by air, kinetic energy is strictly lost through friction with the snow. The kinetic friction force Fk is mu, the kinetic friction coefficient, times the normal to the surface, in that case the total weight M*g of the skier. The total work the friction does against the skier is thus Fk times x, where x is the distance over which the friction force acted. Remembering the formula for kinetic energy, the principle of energy conservation thus dictates the following equality :
1/2*M*v^2 = mu*M*g*x
We see the total mass of the skier becomes irrelevent since it cancels out of the right and left hand side of the equality. Therefore, the speed at which the skier was going before starting to slow down is
v = sqrt(2*mu*g*x)
and since
mu = 0.050
g = 9.81 m/s^2
x = 21 m
then v = 4.539 m/s, which is equivalent to 16.332 km/h once you multiply by 3.6 km/h per m/s.
The coefficient of kinetic friction between wool felt and aluminum is about 0.24 to 0.26.
coefficient kinetic
Ukn
static usully greater then kinetic
The coefficient of static or kinetic friction depends on the surfaces that are causing friction. The formula for it is: force of friction over normal force.
0.35, approximately
The coefficient of kinetic energy is a constant for friction acting as a retarding or dissipative force to calculate the total force on the object. The coefficient of friction u is represented in equation by the relation F = u*N, where N is the normal force.
No, coefficient of friction is dependent on the materials in contact, not their mass. However the FORCE of friction will increase as the mass increases in this case.
static friction is higher in most cases, if you're talking about the coefficient of static or kinetic friction
The coefficient of static friction is always larger because it takes more initial force to move an object that is at rest.
It's hard to guess that in advance, though as a general rule you can guess that smooth surfaces have a lower coefficient of friction than rough surfaces, and lubrication usually reduces the friction. However, to get more precise information, this has to be measured. Of course, you can first search the Internet - somebody may already have measured it.
The rougher a surface is, the higher the coefficient of static and kinetic friction will be.