Question

In: Physics

Show that the acceleration of any object down a frictionless incline that makes an angle theta...

Show that the acceleration of any object down a frictionless incline that makes an angle theta with the horizontal is a= g sin theta (note that the acceleration is independent of mass.

Solutions

Expert Solution

This is a very general question and has no certain answer because you don't tell us which direction the force is directed.

I will solve one solution in which the force you mention is the weight of the object

Let
F = the force
m = mass of object (unknown)
g = gravity
a = acceleration down slope
? = angle of slope from horizontal
Fn = normal force of slope on mass
Ff = friction force of slope on mass
Fg = Force of weight (gravity) acting parallel to the slope
? = coefficient of kinetic friction

as stated, the force is the weight of the mass
F = mg

If we draw a free body diagram
The normal force of the slope on the mass is
Fn = Fcos?
Fn = mgcos?

and the weight force acting parallel to the slope is
Fg = Fsin?
Fg = mgsin?

Then the friction force of the slope on the mass is
Ff = ?Fn
Ff = ?mgcos?

So the net force accelerating the mass will be the gravity force parallel to the slope minus the friction force

Fnet = Fg - Ff
Fnet = mgsin? - ?mgcos?
Fnet = mg(sin? - ?cos?)

If we then compare this equation to the basic equation
F = ma
we can see that
a = g(sin? - ?cos?)

which is the acceleration of the mass down the slope with no other external forces acting on it.

If friction is negligable, ? ? 0, and this reduces to

a = gsin?


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