Magnitude of Forces: Block Motion on a Ramp

In summary, the block is sliding up the ramp in situation 1, stationary in situation 2, being dragged up the ramp in situation 3, and sliding downwards at increasing speed in situation 4. The difference between sliding up and being dragged up is that in the former, the block is moving due to its own motion, while in the latter, it is being moved by an external force.
  • #1
jumptheair
16
0

Homework Statement



A block is on a ramp. What is happening to the block for each of the following situations?:
1. fk(down the ramp)
2. fs(up the ramp) < w,x(down)
3. Tension(up) > fk(down) + w,x(down)
4. fk(up) < w,x(down)..FBD also looks like fk(up) magnitude is equal to fs(up) from 2.

choices:
A) a block is sliding down a ramp at increasing speed.
B) a block is being dragged up a ramp.
C) a block is sliding down a ramp at decreasing speed.
D) a block is sliding up a ramp.
E) a block is stationary on a ramp.
F) a block is momentarily at rest; it is changing directions-after sliding up a ramp, it is about to slide back down.

Homework Equations



Newton's second: Fnet=ma

The Attempt at a Solution



This is what i think. Please correct me if I'm wrong at any point. Thanks.

1.A - because both weight and friction pulls it down
2.E - because fs is acting.
3.B - Since tension is greater than the sum of fk and weight that is pulling it down. But
what is the difference between sliding up and being dragged up? Since tension is
making it go up, should it be dragged up?
4.F - momentarily at rest because magnitude of fk is equal to fs from 2. But changes to
downwards because given that fk and not fs is applied.
 
Last edited:
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  • #2
jumptheair said:

Homework Statement



A block is on a ramp. What is happening to the block for each of the following situations?:
1. fk(down the ramp)
2. fs(up the ramp) < w,x(down)
3. Tension(up) > fk(down) + w,x(down)
4. fk(up) < w,x(down)..FBD also looks like fk(up) magnitude is equal to fs(up) from 2.

choices:
A) a block is sliding down a ramp at increasing speed.
B) a block is being dragged up a ramp.
C) a block is sliding down a ramp at decreasing speed.
D) a block is sliding up a ramp.
E) a block is stationary on a ramp.
F) a block is momentarily at rest; it is changing directions-after sliding up a ramp, it is about to slide back down.

Homework Equations



Newton's second: Fnet=ma

The Attempt at a Solution



This is what i think. Please correct me if I'm wrong at any point. Thanks.

1.A - because both weight and friction pulls it down

but friction always acts opposite the direction of motion.

2.E - because fs is acting.

I agree. So is there always a tension involved? Because if fs<w,x the block would be sliding unless there were other forces involved.

3.B - Since tension is greater than the sum of fk and weight that is pulling it down. But
what is the difference between sliding up and being dragged up? Since tension is
making it go up, should it be dragged up?

Yeah, both dragged up and sliding up seem right. I don't understand the difference.

4.F - momentarily at rest because magnitude of fk is equal to fs from 2. But changes to
downwards because given that fk and not fs is applied.
[/quote]

I don't see why... if the object is momentarily at rest, then kinetic friction will not be acting.
 
  • #3
tension is only involved in 3. These are the given FBD:
1. http://www.learning.physics.dal.ca/library/Graphics/Gtype10/blockfbd1.gif
2. http://www.learning.physics.dal.ca/library/Graphics/Gtype10/blockfbd6.gif
3. http://www.learning.physics.dal.ca/library/Graphics/Gtype10/blockfbd2.gif
4. http://www.learning.physics.dal.ca/library/Graphics/Gtype10/blockfbd3.gif
 
Last edited by a moderator:
  • #4
For 1, as you see in the FBD, only fk is drawn. I don't know if ALL forces are drawn in but without a pushing force, the fk and gravity will bring it down right? I am not sure for which cases but i remember that friction doesn't ALWAYS oppose motion. I am confused.

For 4, the fk is drawn so that it is equal to fs from #2. Um.. it's not possible unless there is other forces not drawn that are applied to the block, right?
 
  • #5
jumptheair said:
For 1, as you see in the FBD, only fk is drawn. I don't know if ALL forces are drawn in but without a pushing force, the fk and gravity will bring it down right?

Not necessarily. It could be sliding upwards and decelerating.

Im not sure for which cases but i remember that friction doesn't ALWAYS oppose motion. I am confused.

Hmmm... as far as I know, static friction prevents motion, and kinetic friction acts against the direction of motion.

For 4, the fk is drawn so that it is equal to fs from #2. Um.. it's not possible unless there is other forces not drawn that are applied to the block, right?

In 4, it seems to me it is sliding downwards since kinetic friction is acting upwards.
 
  • #6
Ok. I am convinced that 1. is sliding up the ramp.
If 4 is sliding downwards, would it be going down at increasing speed because w,x is greater in magnitude than fk so Fnet is positive (downwards) so that acceleration is also positive(downwards)?
 
  • #7
jumptheair said:
Ok. I am convinced that 1. is sliding up the ramp.
If 4 is sliding downwards, would it be going down at increasing speed because w,x is greater in magnitude than fk so Fnet is positive (downwards) so that acceleration is also positive(downwards)?

yes.
 

1. What is the magnitude of the force required to move a block on a ramp?

The magnitude of the force required to move a block on a ramp depends on several factors such as the mass of the block, the angle of the ramp, and the coefficient of friction between the block and the ramp. It can be calculated using the equation F = mgsinθ + μmgcosθ, where F is the force, m is the mass, g is the acceleration due to gravity, θ is the angle of the ramp, and μ is the coefficient of friction.

2. How does the angle of the ramp affect the magnitude of the force required?

The angle of the ramp has a direct impact on the magnitude of the force required to move a block. As the angle of the ramp increases, the force required to move the block also increases. This is because the component of gravity pulling the block down the ramp (mgcosθ) increases with a steeper angle, requiring a larger force to counteract it.

3. What role does mass play in determining the magnitude of the force required?

The mass of the block is a crucial factor in determining the magnitude of the force required to move it on a ramp. The greater the mass of the block, the greater the force needed to overcome its inertia and move it up the ramp. This can be seen in the equation F = mg, where F is directly proportional to the mass (m).

4. How does friction affect the magnitude of the force required to move a block on a ramp?

The coefficient of friction between the block and the ramp plays a significant role in determining the magnitude of the force required to move the block. A higher coefficient of friction means there is more resistance between the surfaces, requiring a larger force to overcome it and move the block. This is represented in the equation F = μmgcosθ, where the force (F) is directly proportional to the coefficient of friction (μ).

5. Can the magnitude of the force required to move a block on a ramp be reduced?

Yes, the magnitude of the force required to move a block on a ramp can be reduced by decreasing the angle of the ramp or by reducing the coefficient of friction between the block and the ramp. Additionally, using a pulley system or adding lubrication to the ramp can also reduce the force needed to move the block. However, the mass of the block will always play a role in determining the minimum amount of force required to move it on a ramp.

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