Acceleration of mass on an incline plane

Click For Summary

Homework Help Overview

The discussion revolves around a physics problem involving a block being pushed up a frictionless incline by a horizontal force. The incline makes an angle of 31° with the horizontal, and participants are tasked with finding the acceleration of the block. The problem involves concepts from dynamics, particularly forces acting on an object on an incline.

Discussion Character

  • Mixed

Approaches and Questions Raised

  • Participants discuss the calculation of the force components acting on the block, questioning the validity of the original poster's approach to resolving the forces involved. There is mention of the gravitational force component and its effect on the block's acceleration.

Discussion Status

The discussion is ongoing, with various participants providing feedback and questioning assumptions made in the original calculations. Some participants express confusion over the treatment of force components and the equations used, while others attempt to clarify the relationships between the forces acting on the block.

Contextual Notes

There are indications of miscommunication and differing interpretations of the problem setup, particularly regarding the coordinate system and the definitions of forces involved. Some participants note that the original poster's equations may have been misapplied, leading to incorrect conclusions.

gergerger
Messages
4
Reaction score
0

Homework Statement



A horizontal force of 100 N pushes a 17 kg block up a frictionless incline that makes an angle of 31° with the horizontal.

Find the acceleration of the block.

Homework Equations



F = ma

F_g = mg

The Attempt at a Solution



Cos31 = 100/(component of force along plane) --> 100/cos31 = F --> F = 166.77N

Then I used this in my F = ma equation producing.

(116.77)N = (17)kg (a)

a = 6.86

This is the wrong answer.
 
Last edited:
Physics news on Phys.org
gergerger said:

Homework Statement



A horizontal force of 100 N pushes a 17 kg block up a frictionless incline that makes an angle of 31° with the horizontal.

Find the acceleration of the block.

Homework Equations



F = ma

Fg = mg

The Attempt at a Solution



Cos31 = 100/(component of force along plane) --> 100/cos31 = F --> F = 166.77N
the component of the force cannot be greater than the force itself. Recheck that equation.
Then I used this in my F = ma equation producing.

(166.77)N = (17)kg (a)

a = 6.86

This is the wrong answer.
What happened to the component of the weight acting along the plane?
 
your second relevant equation is wrong (how can Fg=mg or F=m unless a=1?)

and the first step of the soln is also wrong...
how come component surpasses the force itself?Then solve(without forgetting weight components)...EDIT:: maybe me and phantomjay answered in quite near time gaps!
 
@Jay, Firstly, the force was already broken up, so yes the component of the force in the direction of the plane can indeed be bigger than the force in the x direction. I'm not sure what to do about the component of weight, that's rather why I posted the question. You answered nothing.

@Legend. Please, don't post where you have nothing useful to say. It isn't F times g, it's F subg meaning the component of force that is caused by gravity is equal to the mass of an object times acceleration due to gravity. Please, say no more. /facedesk
 
Gegerger: First - copping an attitude is not a good way to get help. Second, your initial post was, apparently, not clear - as legend, Jay, and I all seem to have understood the problem in the same manner. Third - your math is simply wrong in the last step - I'm not sure how you got a value of 6.86. Maybe you input 116.77, as opposed to 166.77?
 
gergerger said:
@Jay, Firstly, the force was already broken up, so yes the component of the force in the direction of the plane can indeed be bigger than the force in the x direction. I'm not sure what to do about the component of weight, that's rather why I posted the question. You answered nothing.
we don't give answers here, only help, to those who want it.
@Legend. Please, don't post where you have nothing useful to say. It isn't F times g, it's F subg meaning the component of force that is caused by gravity is equal to the mass of an object times acceleration due to gravity. Please, say no more. /facedesk
Chill, you made an error denoting F_g as Fg. So be it. I've done it many times. It happens to the best of us.
 
About that help thing... Where is it exactly?

Oh, and whoever said that my math was wrong, it was... sort of. I did use 116.77 in my calculations and that is the right number. I wrote it wrong in the original post. /goes to fix
 
gergerger said:
About that help thing... Where is it exactly?

By help, we point you in the right direction. We don't do your work for you.

Now, to clear everything up, please describe the coordinate system you are using so we can all get on the same page.
 
gergerger said:
@Jay, Firstly, the force was already broken up, so yes the component of the force in the direction of the plane can indeed be bigger than the force in the x direction. I'm not sure what to do about the component of weight, that's rather why I posted the question. You answered nothing.

@Legend. Please, don't post where you have nothing useful to say. It isn't F times g, it's F subg meaning the component of force that is caused by gravity is equal to the mass of an object times acceleration due to gravity. Please, say no more. /facedesk

Wow... Was going to help you but when I read this I don't want to waste my time. Way to treat the ones that are trying to help you do your freaking homework.
 
  • #10
@Inferior, then why post? Gtfo already. Anyway, I didn't use a coordinate system jhae. If you have a suggestion about how to use one, please explain. ;)
 
  • #11
Perhaps it's time for you to rethink your participation on this forum, gergerger.
 
  • #12
I'm sorry, but did no one realize he had his equation for cosine upside down, or is that what PhanthomJay was trying to imply when he said "recheck that equation"? I just thought it might seem a little more straightforward of an approach to point out his error.

Also, as far as the answer goes, don't forget to include the component of the object's weight acting down the plane when you calculate your net force. The net force should be the difference between the 85.7N push parallel to the incline and the parallel component of the weight (170Nsin31, 87.6N). The block in fact should slide down the incline, with an acceleration 0.11 m/s/s.

The component of the 100N force acting into the plane only increases the normal force and does not cause it to accelerate into the inclined plane. If it were a real incline with friction, however this "perpendicular" component would increase the force of friction as well, which would also be included in your net force. Did that help at all? Are you remembering to turn your head sideways and redefine "horizontal" and "vertical"?
 

Similar threads

Block on top of an inclined plane, with a rough surface, that moves with constant acceleration
  • · Replies 41 ·
2
Replies
41
Views
4K
Newton's law problem: Pushing 2 stacked blocks on a horizontal table
  • · Replies 13 ·
Replies
13
Views
3K
Finding the acceleration of a block on an inclined plane with friction
  • · Replies 2 ·
Replies
2
Views
783
Find acceleration of Moving incline with a block on it
  • · Replies 11 ·
Replies
11
Views
3K
Block and pulley on movable incline
  • · Replies 2 ·
Replies
2
Views
2K
Friction direction change in a inclined circular bend (car on a road)
  • · Replies 11 ·
Replies
11
Views
1K
A block lies on an inclined plane with an angle of elevation
  • · Replies 16 ·
Replies
16
Views
5K
Compute acceleration on an inclined plane with friction
  • · Replies 5 ·
Replies
5
Views
2K
I have a hard time with kinematics involving inclined planes
  • · Replies 4 ·
Replies
4
Views
2K
How do I find acceleration and tension on an inclined plane
  • · Replies 1 ·
Replies
1
Views
2K