Examkin

Question

Difficulty: MediumFriction and Resistance

A mason is pushing a solid, uniform rectangular clay brick across a horizontal wooden scaffold plank at a constant speed. Initially, the brick is positioned so it slides while resting flat on its widest face. If the mason stands the brick up so it slides on its narrowest face across the same section of the plank, how will the kinetic frictional resistance change?

  1. It will remain unchanged because kinetic friction depends on normal force and surface materials, not contact area.Answer
  2. B
    It will decrease because there is less surface area rubbing against the wooden plank.
  3. C
    It will increase because the brick's total weight becomes concentrated, increasing the total normal force.
  4. D
    It will decrease because altering the brick's orientation reduces its resistance to changes in motion.

Answer

The kinetic frictional resistance will remain unchanged.
For standard rigid objects, the kinetic frictional force is determined solely by the nature of the materials in contact (the coefficient of friction) and the total force pressing them together (the normal force). Because the brick's mass and the materials involved do not change when it is rotated, the overall frictional resistance remains exactly the same, regardless of how much surface area is touching the plank.

Step-by-Step Solution

1
Identify the formula for kinetic friction.
Fk=μk×NF_k = \mu_k \times N
To determine exactly which physical variables affect the frictional force.
2
Analyze the normal force (NN).
The normal force equals the weight of the brick (N=mgN = mg), which remains constant regardless of its orientation.
To see if rotating the brick changes the total downward force pressing the surfaces together.
3
Analyze the coefficient of kinetic friction (μk\mu_k).
The coefficient remains constant because the materials (clay and wood) and their surface properties have not changed.
To verify that the fundamental physical interaction between the two specific surfaces remains the same.
4
Evaluate the effect of surface contact area.
Surface area is not a variable in the standard kinetic friction formula.
To conclusively confirm that resting the brick on a narrower face does not alter the total frictional resistance.

Key Concept

Independence of Friction from Surface Area
Rate this question

Topics

Friction and Resistance

More questions from this topic