Friction

Step 1: Understanding the Concept:
Friction is a non-conservative force. Work done by non-conservative forces over a closed path is not zero.

Step 2: Detailed Explanation:
1. Work-energy theorem is valid in all inertial frames.
2. Work-energy theorem can be derived from Newton's second law.
3. Work is a scalar quantity.
4. Friction dissipates energy, so work done over a closed path is negative, not zero.
5. Friction opposes motion, so work done is negative.

Step 3: Final Answer:
The false statement is that work done by friction over a closed path is zero.

Step 1: Understanding the Concept:
Coefficients of friction depend only on the nature of the surfaces, not on the area of contact.

Step 2: Detailed Explanation:
and are dimensionless constants. They do not depend on the area of contact.
Friction force = coefficient normal force, independent of area.

Step 3: Final Answer:
and are independent of A.

Step 1: Understanding the Concept:
When a block slides on a rough surface, kinetic friction exerts a constant force opposing the motion, causing constant deceleration. The stopping distance can be found using kinematics equations or the Work-Energy Theorem. We will use kinematics.

Step 2: Key Formula or Approach:
1. Find the frictional force:
2. Find the acceleration (deceleration):
3. Use the kinematic equation relating velocity, acceleration, and distance:

Step 3: Detailed Explanation:
Given values:
Mass, kg
Coefficient of kinetic friction,
Initial velocity, m/s
Final velocity, m/s (since it stops)
Let's assume the acceleration due to gravity m/s for standard calculation (or m/s , but is common when not specified to yield clean numbers).
The acceleration is:

Now, substitute the knowns into the kinematic equation:





(If m/s was intended, m/s , and m).

Step 4: Final Answer:
The stopping distance is 25 meters.

Concept:
Physics - Work-Energy Theorem or Kinematics with Friction.
Step 1: Find the frictional force and acceleration.
The kinetic frictional force is . The acceleration (deceleration) produced by friction is: $ \mu_k = 0.2 g = 10 u 10~ms^{-1} v 0~ms^{-1} a -2~ms^{-2} $