Newton's laws and inclined plane with friction

[CURMC]

Homework Statement

A person with a mass of M is on top of a platform with wheels, they fall in solidarity through the inclined plane of angle theta. There is no friction between the platform and the inclined plane(ideal wheels), but there is friction between the person and the platform.
Find the friction force the platform applies to the person

Relevant Equations

none

im having trouble writing the newton ecuations, i do not understand how the friction force is applied to the person. I wrote this:
The coordinates that i choose are X in the direction of the movement, and Y perpendicular to X
Forces applied to the person are the Normal force NA (vertical and up), the persons weight PA (vertical and down)
forces applied to the platform : Normal Force NB (perpendicular to the inclined plane) the platforms weight PB(vertical and down)

The thing is the excersise does not have any data of how much the weights are or the angle theta or the coeficients, and i do not understand if the friction force is horizontal on the person or it is in the opposite direction of the inclined plane

Sorry for my bad english, i tried to explain it the best way possible

 

[anuttarasammyak]

The thing is the excersise does not have any data of how much the weights are or the angle theta or the coeficients, and i do not understand if the friction force is horizontal on the person or it is in the opposite direction of the inclined plane

The data is not written suggests that they do not matter, a big hint from your teacher, I suppose,
We may check our reasoning by our experience of jet coaster ride or ging a down smooth slope on bycycle with/without braking.

 

[kuruman]

This is the problem with no numerical answer. You are expected to provide an answer in symbolic form.
You already know that the symbol for the mass of the person is $M$. You also know that the acceleration of gravity is $g$. You are not given the angle of the incline, so assume that it is $\theta.$ You may also assume that the platform has no mass or that $M$ is the combined mass of the person and the platform.

Can you find an algebraic expression for the acceleration $a$ in terms of $M$, $g$ and $\theta~$?

Forces applied to the person are the Normal force NA (vertical and up), the persons weight PA (vertical and down)

What about the force of friction between the person and the platform which is what you are looking for?

 

[erobz]

Homework Statement: A person with a mass of M is on top of a platform with wheels, they fall in solidarity through the inclined plane of angle theta. There is no friction between the platform and the inclined plane(ideal wheels), but there is friction between the person and the platform.
Find the friction force the platform applies to the person
Relevant Equations: none

im having trouble writing the newton ecuations, i do not understand how the friction force is applied to the person.

You can imagine the person at rest on the platform on the slope ( think of something externally holding the platform in place) as a thought experiment. How is the friction force applied to the body of the person in that scenario, and what would it be?

Then the interesting bit comes after you make the system a little more inclusive (say the person and the platform ) and assume they stay at rest w.r.t. each other as they roll down the slope. What would be their acceleration down the slope?

Finally, you look at the first system again ( just the person and the external forces acting on them) as they accelerate down the slope at the rate you found w.r.t. to in inertial frame of reference fixed at some convenient location on the slope to determine what must be happening to $f$.

 

[haruspex]

You are not given the angle of the incline

We are:

through the inclined plane of angle theta.

Forces applied to the person are the Normal force NA (vertical and up),

The normal force between two bodies is, by definition, normal to the plane of contact of the bodies (if that is well defined). The question setter seems to expect you to assume the platform the person sits on is parallel to the plane, though that is not necessarily the case.

i do not understand if the friction force is horizontal on the person or it is in the opposite direction of the inclined plane

Likewise, the friction force is, by definition, parallel to the plane of contact.