Calculate the force of ball on an incline leaning on a wall

Click For Summary

Homework Help Overview

The problem involves a ball resting on an inclined plane that also touches a vertical wall. The ball's weight and the angle of the incline are given, and the objective is to determine the force exerted by the ball on the wall. The discussion centers around the forces acting on the ball, particularly the gravitational force and the components of the forces from the incline and the wall.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants explore the forces acting on the ball, including gravity and the reactions from the incline and wall. Questions arise regarding the ability of the vertical wall to counteract gravitational forces and the nature of the forces involved.

Discussion Status

Participants are engaging in a dialogue about the forces at play, with some suggesting that only the incline can provide the necessary vertical force to counteract gravity. There is a focus on understanding the relationship between the forces and the implications of the angle of the incline.

Contextual Notes

There is mention of neglecting friction in the problem, which influences the discussion about the forces and their components. Participants also reference a diagram that is not included in the text, which may be crucial for visualizing the problem.

Amit86
Messages
8
Reaction score
0
Hi all,

I'm working on a problem from the Feynman exercise book, and have been racking my brains for an answer, so would really appreciate some help here. The problem seems simple enough:

A ball with a 3cm radius, weighing 1kg rests on an inclined plane (angle alpha) and also touches a vertical wall. Neglect friction.

(see attached diagram)

What is the force of the ball acting on the wall (Fw)?

The answers in the back gives
Fw= tan(alpha) kg.wt

I got the force due to gravity acting down the plane, Fr = 9.81.sin(alpha). The horizontal component of this force, which to my mind is the force acting on the wall, is

Frhor=9.81* sin(alpha)cos(alpha)

What am I missing here?!

Thanks!

Amit
 

Attachments

  • ball in corner problem.png
    ball in corner problem.png
    847 bytes · Views: 1,065
Physics news on Phys.org
Amit86 said:
Hi all,

I'm working on a problem from the Feynman exercise book, and have been racking my brains for an answer, so would really appreciate some help here. The problem seems simple enough:

A ball with a 3cm radius, weighing 1kg rests on an inclined plane (angle alpha) and also touches a vertical wall. Neglect friction.

(see attached diagram)

What is the force of the ball acting on the wall (Fw)?

The answers in the back gives
Fw= tan(alpha) kg.wt

I got the force due to gravity acting down the plane, Fr = 9.81.sin(alpha). The horizontal component of this force, which to my mind is the force acting on the wall, is

Frhor=9.81* sin(alpha)cos(alpha)

What am I missing here?!

Thanks!

Amit
Hello Amit86. Welcome to PF !

ball-in-corner-problem-png.85133.png


The only forces acting on the ball are gravity, and the two forces supplied by the two surfaces. Right ?

Can the vertical wall counteract the force gravity exerts on the ball?
 
Hi, Sammy. That's correct.
 
Amit86 said:
Hi, Sammy. That's correct.
There are two questions I asked.
 
I imagine the vertical wall can counteract the force
 
Amit86 said:
I imagine the vertical wall can counteract the force
(By the way, there is a "Reply" feature in the lower right-hand corner of the message screen that's helpful with dialogue.)

Can the vertical surface produce a force on the ball that has a vertical component?

(There's no friction.)
 
SammyS said:
(By the way, there is a "Reply" feature in the lower right-hand corner of the message screen that's helpful with dialogue.)

Can the vertical surface produce a force on the ball that has a vertical component?

(There's no friction.)
As far as I can tell, I don't think it can. "both surfaces have negligible friction"
 
Amit86 said:
As far as I can tell, I don't think it can. "both surfaces have negligible friction"
Right.

Therefore, only the incline can provide a force which has the vertical component necessary to counter act the gravitational force. Right?
 
SammyS said:
Right.

Therefore, only the incline can provide a force which has the vertical component necessary to counter act the gravitational force. Right?
I suppose that's true.
 
  • #10
You say things like "I imagine", "as far as I can tell", and "I suppose". Do you know in what direction gravity acts? Do you know in which direction the force from the wall acts?
 
  • #11
HallsofIvy said:
You say things like "I imagine", "as far as I can tell", and "I suppose". Do you know in what direction gravity acts? Do you know in which direction the force from the wall acts?

Of course I do; check the diagram. I am looking for some insight into where the tan(alpha) comes from. I've provided all the information given in the question, I need to get some sense of how to proceed with a solution, and would appreciate constructive advice.
 
  • #12
SammyS said:
Right.

Therefore, only the incline can provide a force which has the vertical component necessary to counter act the gravitational force. Right?
This should help you to find the vertical force the incline needs to exert on the ball.
 
  • #13
SammyS said:
This should help you to find the vertical force the incline needs to exert on the ball.
okay thanks!
 
  • #14
Amit86 said:
okay thanks!
Ok so I think I've got then...

The vertical component of the reaction force of the plane = the total gravitational force (i.e 9.81 x 1kg), so the horizontal component of reaction force of the plane would be 9.81*tan alpha Newtons or

Fw= tan(alpha) kg wt

Thanks for your help!
 
  • #15
Amit86 said:
Ok so I think I've got then...

The vertical component of the reaction force of the plane = the total gravitational force (i.e 9.81 x 1kg), so the horizontal component of reaction force of the plane would be 9.81*tan alpha Newtons or

Fw= tan(alpha) kg wt

Thanks for your help!
Correct !

Notice that this vertical force is greater than the vertical force that the incline exerts for the case when the ball is allowed to roll.
 
Last edited:

Similar threads

Rope between inclines with maximum length of hanging middle portion
  • · Replies 46 ·
2
Replies
46
Views
7K
Determining the angle while dealing with friction on an inclined plane
  • · Replies 8 ·
Replies
8
Views
3K
How Does a Dog Running on a Ball Affect Its Motion on an Inclined Plane?
  • · Replies 11 ·
Replies
11
Views
2K
Which Force is Represented by the Gradient of the Ball-Wall Collision Graph?
  • · Replies 3 ·
Replies
3
Views
4K
Why is the direction of kinetic/static friction up a ramp?
  • · Replies 7 ·
Replies
7
Views
2K
A box over an inclined plane with a mass, no friction
  • · Replies 1 ·
Replies
1
Views
1K
Calculating Theoretical Reaction Force of Ball Traveling in Semi-Circle
  • · Replies 43 ·
2
Replies
43
Views
4K
Which Path is Quickest? Investigating Ball Bearings on an Inclined Tube
  • · Replies 14 ·
Replies
14
Views
3K
Max Upward Force to Hold Bowling Ball on Wall
  • · Replies 20 ·
Replies
20
Views
7K
Block at rest on an inclined surface
  • · Replies 36 ·
2
Replies
36
Views
6K