Block held against wall, force problem

In summary, a 12 N horizontal force is applied to a block weighing 5.0 N against a vertical wall. The coefficients of static and kinetic friction are 0.60 and 0.40 respectively. The block will not move initially due to the calculated maximum kinetic friction force being less than its weight. In unit-vector notation, the force on the block from the wall is (-12i + 5j) Newtons, with the 5j component representing the normal force caused by friction. Removing the wall would eliminate this 5j component.
  • #1
azure kitsune
65
0

Homework Statement



A 12 N horizontal force F pushes a block weighing 5.0 N against a vertical wall. The coefficient of static friction between the wall and the block is 0.60, and the coefficient of kinetic friction is 0.40. Assume that the block is not moving initially. (a) will the block move? (b) in unit-vector notation, what is the force on the block from the wall?

Homework Equations



f = (mu) * N

The Attempt at a Solution



For (a), I just calculated fk, max and since it is greater than the weight of the block, the block will not move.

I'm confused about part (b). The answer at the back of the book is (-12i + 5j) Newtons. I understand the 12i part. That's just the normal force of the wall on the block. But where does the 5j come from? I thought the 5 Newtons upwards were due to the friction and not the wall exerting a force on the block?
 
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  • #2
azure kitsune said:
[...] I thought the 5 Newtons upwards were due to the friction and not the wall exerting a force on the block?


If this is so, then if the wall were removed then would the 5 Newtons still be present?
Yes the 5 Newtons is due to the friction, however the friction is due to the normal force.
So your -12i and your 5j are both caused by the same entity essentially.
 
  • #3
Oh, duh! The friction is also a force from the wall. Thanks for your help. =)
 
  • #4
fk, max = uk*N = .4*12 = 4.8 N which is less than the weight of the block, no?
 

What is the definition of force?

Force is a physical quantity that describes the strength or intensity of an interaction between two objects. It can cause an object to accelerate or change its motion.

What is the difference between weight and mass?

Weight is a measure of the force of gravity on an object, while mass is a measure of the amount of matter an object contains. Weight can vary depending on the strength of the gravitational pull, while mass remains constant.

How is friction related to force?

Friction is a force that resists the motion of objects in contact with each other. It acts in the opposite direction of the motion and can affect the amount of force needed to move an object.

How does the angle of the block against the wall affect the force required to hold it in place?

The angle of the block against the wall affects the force required to hold it in place because it changes the direction of the force. The force needed to hold the block in place is equal to the weight of the block multiplied by the cosine of the angle between the block and the wall.

What factors can affect the force needed to hold the block against the wall?

The force needed to hold the block against the wall can be affected by the weight of the block, the angle of the block against the wall, and the coefficient of friction between the block and the wall. Other factors such as surface conditions and air resistance can also have an impact on the required force.

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