The question in the uploaded image concerns the dynamic friction force, and it asks which of the given statements is NOT true about it. Here's the transcription and analysis:

Question (translated):
The dynamic friction force, which arises at the contact surface between a sliding object and the supporting plane, has a magnitude $F_f = \mu \cdot F_N$.
Which of the following statements is NOT true about this force?

1. Its intensity increases linearly with the sliding velocity.
2. It is a constant force along the motion.
3. It is a dissipative force and performs negative work.
4. It is always directed along the tangent to the trajectory, opposite to the displacement direction.

Answers:
A) 1
B) 2
C) 3
D) 4

Explanation:

• Dynamic friction force: It depends on the coefficient of dynamic friction $\mu$ and the normal force $F_N$.
  • $F_f = \mu \cdot F_N$, which does not depend on the velocity.
  • The force is constant in magnitude as long as $F_N$ and $\mu$ remain constant.

Analysis of the statements:

1. "Its intensity increases linearly with the sliding velocity":

   • FALSE: The dynamic friction force is independent of velocity and remains constant for a given $F_N$ and $\mu$.
   • This is the correct answer, as the question asks for the false statement.

2. "It is a constant force along the motion":

   • TRUE: The dynamic friction force has a constant magnitude and direction for a given $F_N$ and $\mu$.

3. "It is a dissipative force and performs negative work":

   • TRUE: Friction opposes motion, removing mechanical energy from the system, and performs negative work.

4. "It is always directed along the tangent to the trajectory, opposite to the displacement direction":

   • TRUE: By definition, friction always acts along the tangent to the surface, in the direction opposite to the motion.

Final Answer:

The statement that is NOT true is:
1. Its intensity increases linearly with the sliding velocity.

Correct Option: A (1)

Would you like further details or additional explanations?

Here are some related questions to deepen understanding:

1. How does the coefficient of friction $\mu$ differ between static and dynamic friction?
2. Why does dynamic friction remain constant while static friction varies?
3. What are some examples of dissipative forces besides friction?
4. How does the normal force $F_N$ affect the magnitude of dynamic friction?
5. How can the work done by friction be calculated in a given displacement?

Tip: Always remember that friction depends on the properties of the surface and the normal force, but dynamic friction is independent of velocity!