Solving the Kinetic Friction Problem - Bob's Dilemma

In summary, Bob needs to push a crate with a weight of 800N and a coefficient of kinetic friction of 0.5. He wants to know if a force of 100N is enough to move the crate. Based on the equation for kinetic friction, the force needed to move the crate is 400N. Even if the crate is already moving, 100N is not enough force to keep it moving. Additionally, the static friction is always greater than the kinetic friction, so the crate is even harder to move if it starts from rest.
  • #1
brayrbob
24
0
I need help with this problem
Bob wants to push a crate horizontally with a force of 100N. If the coefficient of kinetic friction between the crate and the floor is 0.5 and the crate has a weight of 800 N, can he move the crate.

Okay that's the problem and I don't believe that 100N is enough force to push a crate of 800N. But even if my answer is wrong I'm not sure which equation to use to prove it.
When I take the kinetic friction of 0.5 and times it by the crate's 800N, I get 400N. Is this the way to show that 100N is not enough force to push this crate?
 
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  • #2
Yep, sounds ok to me.
 
  • #3
Even assuming the crate is already moving, it wouldn't be enough.
The force of kinetic friction as you showed is eqaul to the objects normal force times the coefficient of kinetic friction, whcih equals 400 N.
If the pusher only supplies 100 N, then the box will slow to a stop if it is already moving.

Generally (from everything I have seen), the static friction is always higher than the kinetic friction, so if the crate starts from rest, the pusher will have even less of a chance to move the box.
 
  • #4
Okay, That answer seemed logical to me, but I wanted to be sure I was right.
Thank you all very much for your help.
 
  • #5
If the problem only gives you the kinetic friction constant then, like someone mentioned above, you can say that the static friction coefficient is always larger then the kinetic friction coefficient. Therefore the 100N would not be larger then the static frictional force which is larger then 400N.
 

1. What is kinetic friction?

Kinetic friction is the force that resists the motion of two surfaces sliding against each other. It is caused by the microscopic irregularities on the surface of objects.

2. How is kinetic friction calculated?

Kinetic friction is calculated by multiplying the coefficient of kinetic friction, which is a measure of the roughness of the surfaces, by the normal force, which is the force perpendicular to the surfaces.

3. What is the coefficient of kinetic friction?

The coefficient of kinetic friction is a unitless value that represents the roughness of two surfaces in contact. It is typically denoted by the symbol μ and can range from 0 to 1, with 0 being a completely smooth surface and 1 being a very rough surface.

4. How can I solve a kinetic friction problem?

To solve a kinetic friction problem, you will need to know the coefficient of kinetic friction, the normal force, and the mass of the object. You can then use the formula Fk = μkN to calculate the force of kinetic friction.

5. How does kinetic friction affect an object's motion?

Kinetic friction acts in the opposite direction of an object's motion, slowing it down and causing it to eventually come to a stop. It also converts some of the object's kinetic energy into heat, causing a decrease in its overall energy.

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