Simple physics problem. BEST ANSWER soon :)?

Question

A 20kg person starts from rest and reaches 4.0m/s at the bottom of a 20.0degree slide of length 4m. What is the coefficient of sliding friction?

Answer 1

Well, this problem really makes more sense when you draw it out. So draw an inclined plane on your paper with a 20degree angle at the bottom and a person near the top.

The hypotenuse of the triangle is 4 m. Now from the person, you need to draw a line going straight down to represent gravity and a line going through the top of the person's head to represent the perpendicular force.

This triangle is now similar to the orginial, and the angle by the person is 20 degrees. and the line representing gravity is equal to mass x acceleration (200). This line is now the hypotenuse of that triangle. You can you this to find the "x" part of his weight.

Thus 200sin20 which is equal to 68.4 N.

Remember your equation for Friction is F=uN. the 68.4 is your "N" value.

Now you need to find your "F" value. F=ma.

To find "a," use kinematics.

Vf=4m/s

Vo=0m/s

d=4m

Vf^2=Vo^2 +2ad

Thus, a=2

Now, use this to find F.

F=ma=20x2=40.

Finally, go back to F=uN

40=u68.4

u=.58

Answer 2

there are two forces acting on the person

1) positive acceleration due to gravity - but only the 20 degree component of it = gsin20

2) negative acceleration (retardation) due to friction = -f

using the equation v^2-u^2 = 2aS and setting initial velocity u as zero

v^2 = 2*(gsin20-f)*S

4^2 = 2*(10sin20-f)*4

10sin20-f = 2

f = 10sin20 - 2 = 1.42

mu = f/r = 1.42/gcos20 = 1.42/9.4 = 0.151

Answer 3

why don't you do your own homework by yourself. and if it's so simple...do it !