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i know that you have to find the mass i order to solve this problem, but is it even possible and how??

a box is sliding down an incline of 38.8 degress at constant velocity. What's the coefficient of friction?

Thanks for your help!

2006-10-10 11:28:28 · 5 answers · asked by Anonymous in Science & Mathematics Physics

5 answers

I disagree, I contend you do not need to know the mass of the box...it ends up canceling in the end.

Think about what the phrase, "at constant velocity" means.
When an object is moving with a constant velocity it means there is no acceleration, and when there is no acceleration the net force acting on the box equals zero.

What forces are acting on the box?
Obviously there is a frictional force which is acting up the slope to oppose the motion of the box down the slop;
There is also a force which is acting down, parallel, to the slope which is acting to pull the box down.

The force parallel to the slop equals,
F_p = mg * sin (theta)
Where theta is the inclination of the ramp.

The force of friction equals the normal force * the coefficient of friction.
The normal force equals,
F_n = mg * cos (theta)
So the frictional force equals,
F_f = mg*cos(theta) * coefficient of friction

Since there is no net force acting on the box the force parallel to the ramp must equal the force of friction,
F_p = mg * sin (theta) = F_f = mg*cos(theta) * coefficient of friction
m and g cancel out and you are left with
sin (theta) = cos(theta) * coefficient of friction
You are given the angle of inclination of the ramp (theta) so just solve for the coefficient.

μ = cos (theta) / sin (theta) = tan (theta)

2006-10-10 11:45:05 · answer #1 · answered by mrjeffy321 7 · 0 0

You don't need to know the mass. The coefficient of friction is the ratio of the friction force to the normal force (force normal to the surface). The normal force exerted by an object of weight X on a slope is X*COS(angle). The force parallel to the surface is X*SIN(angle). With constant-velocity sliding the friction force equals the parallel force due to the weight. So the coefficient of friction = X*SIN(angle)/(X*COS(angle)) = SIN(angle)/COS(angle), or TAN(angle).

2006-10-10 11:43:31 · answer #2 · answered by kirchwey 7 · 0 0

As u know it that it has constant velocity so its acceleration will be zero thus F net = F friction
thus by drawing the inclined plane
So by taking the horizontal vector : mgsin(x)
mgsin(x)=F net [u= mew ; coefficient of friction)
F net = u F normal
F normal =mgcos(x)
equating
mgsin(x)=u*mgcos(x)
u=sin(x)/cos(x)
u=tan(x)
u=tan 38.8
here u go now u will find the ans as no mass is needed

2006-10-10 11:55:42 · answer #3 · answered by Anonymous · 0 0

You don't need to know the mass - it will cancel out.

The restraining force of kinetic friction is given by
Ff = mu*N = mu*m*g*cos38.8

The component of the mass's weight that points down the slope is a force, Fd, trying to accelerate the mass. It is given by
Fd = m*g*sin38.8.

Since the mass is at constant velocity, there are no unbalanced forces - the force of friction, Ff, and the force pointed down the slope, Fd, balance each other so,
mu*m*g*cos38.8 = m*g*sin38.8

Solve for mu

2006-10-10 14:29:34 · answer #4 · answered by sojsail 7 · 0 0

Go to Discovery channel and look up E=Mc2 and you will find the person that came up with E, M, C2

2006-10-10 11:54:50 · answer #5 · answered by creditloandone 1 · 0 1

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