Calculating Coefficient of Friction: Newton's 3rd Law Examples

[honeycoh]

1.) a 50kg block is being pulled at a constant speed along a horizontal surface by a horizontal force of 120N.

Q: what is the coefficient of kenetic friction?

2.) a 100kg wooden crate is being pushed across a wooden floor with a horizontal force of 350N.
Q: What is the net force acting on a crate?

3.) A cabinet weighing 400N is pulled along a horizontal floor at constant speed by a rope which makes an angle of 30 degrees with the floor.

Q: what is the coefficient of sliding friction if the force on the rope is 220N?



Thanks in advance...

 

[aniketp]

Could you show what solving strategy you have applied here?

 

[Moetasim]

I would approach these questions by first understanding the concept of coefficient of friction. This is a measure of the amount of friction between two surfaces in contact with each other. It is a dimensionless quantity and is calculated by dividing the force of friction by the normal force (perpendicular force) between the two surfaces.

1.) To calculate the coefficient of kinetic friction in the first scenario, we need to first determine the force of friction. According to Newton's third law, for every action, there is an equal and opposite reaction. This means that the force pulling the block (120N) is equal to the force of friction acting in the opposite direction. Therefore, the force of friction is also 120N. Now, we can calculate the coefficient of kinetic friction by dividing the force of friction (120N) by the normal force (weight of the block, 50kg x 9.8m/s^2 = 490N). This gives us a coefficient of kinetic friction of 0.24.

2.) In the second scenario, we are given the mass of the crate and the applied force. To determine the net force acting on the crate, we need to consider all the forces acting on the crate. In this case, we have the applied force of 350N and the force of friction acting in the opposite direction. Using Newton's second law (F = ma), we can calculate the net force by subtracting the force of friction (100kg x 9.8m/s^2 = 980N) from the applied force. This gives us a net force of 270N.

3.) In the third scenario, we are given the weight of the cabinet and the force applied by the rope. To calculate the coefficient of sliding friction, we need to first determine the force of friction. Since the cabinet is moving at a constant speed, we know that the force of friction is equal to the force applied by the rope (220N). Now, we can calculate the normal force by using trigonometry and the given angle of 30 degrees. The normal force is equal to the weight of the cabinet (400N) multiplied by the cosine of 30 degrees, which is 346.4N. Finally, we can calculate the coefficient of sliding friction by dividing the force of friction (220N) by the normal force (346.4N), giving us a coefficient of sliding friction of 0.63.

In conclusion