How much force is needed to move the crate?

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Homework Help Overview

The problem involves determining the force required to move a crate that is being pushed at an angle below the horizontal. The crate has a specified weight and a coefficient of static friction with the ground, which are relevant to the calculations of forces involved.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the calculation of the normal force and the frictional force, with one participant attempting to find the normal force by multiplying the mass by gravity. There are suggestions to draw a free body diagram (FBD) to visualize the forces involved. Questions are raised about the relationship between the applied force and the frictional force.

Discussion Status

The discussion is ongoing, with participants exploring different aspects of the problem. Some guidance has been offered regarding the use of free body diagrams and the need to establish equations based on known and unknown forces. There is no explicit consensus yet, as participants are still working through their understanding of the problem.

Contextual Notes

Participants note that they are missing certain values related to the forces acting on the crate, specifically the applied force, kinetic friction, and normal force. There is an emphasis on the absence of acceleration in the vertical direction, which is a key consideration in the analysis.

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Homework Statement



Someone pushes a crate with a force F at 21° below the horizontal. The crate weights 38 kg, and the coefficient of static friction between the crate and the ground is .57. Find the amount of force needed to move the crate.

Homework Equations



f=ma
Fs=(\mus)(Fn)

The Attempt at a Solution



First i tried to find Fn, so i multiplied the mass by 10, and got 380N. Then i added Fsin21 to find Fn...thats about as far as i got haha i don't know what to do after that. i know i need F, but i don't know how to find what it is.
 
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So you know the value of the frictional force.
What force must just be a little bit greater than this frictional force?
 
axlg38 said:

Homework Statement



Someone pushes a crate with a force F at 21° below the horizontal. The crate weights 38 kg, and the coefficient of static friction between the crate and the ground is .57. Find the amount of force needed to move the crate.

Homework Equations



f=ma
Fs=(\mus)(Fn)

The Attempt at a Solution



First i tried to find Fn, so i multiplied the mass by 10, and got 380N. Then i added Fsin21 to find Fn...thats about as far as i got haha i don't know what to do after that. i know i need F, but i don't know how to find what it is.

If you haven't done so, I recommend drawing a free body diagram (FBD). It will help you to visualize what you need.

Also, make a list of what you know and what you don't know.

Can you construct the same number of equations as your unknowns?
 
the force you need to push with?
 
im not exactly sure what i need to know to solve this haha
 
axlg38 said:
im not exactly sure what i need to know to solve this haha

Like I mentioned above, draw out a FBD with your forces. It will help you to see what you need to solve for.
 
already had it drawn out, the only things i seem to be missing are F, Fk, and Fn
 
axlg38 said:
the force you need to push with?
The force you push is at 21 below horizontal. But I asked for the force just to balance the friction and the if two forces are to balance each other they have to be opposite in dir.
Follow advice given and draw the FBD.
 
i did, to the best of my ability
 
  • #10
axlg38 said:
already had it drawn out, the only things i seem to be missing are F, Fk, and Fn

Alright. Remember that there is no acceleration up or down (since the ground is solid). What does this mean to the forces in the vertical direction? Can you write out an equation showing this relation?

What are you looking for in the horizontal direction? Can you write out a relation with the forces you know to create this?

Once you have these 2 equations, solve them simultaneously.
 

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