Its momentum is 2940 because force is equal to change in momentum.but i not sure about the answer ..

The coefficient of friction between the tires of a car and the surface it travels on can be determined by using the given information about the car's mass and the retardation due to friction.

1. Understanding the problem:
- Mass of the car: 400 kg
- Retardation due to friction: 7.35 m/s²

2. The relationship between friction and retardation:
The force of friction acting on the car is responsible for its retardation. This force can be calculated using Newton's second law of motion:
F = m * a
where F is the force, m is the mass, and a is the acceleration (which is the retardation in this case).

3. Calculating the force of friction:
Given that the retardation is 7.35 m/s² and the mass is 400 kg, we can substitute these values into the equation to find the force of friction:
F = 400 kg * 7.35 m/s²
F = 2940 N

4. Calculating the normal force:
The force of friction depends on the normal force, which is the force exerted by the surface on the car perpendicular to it. The normal force is equal to the weight of the car, which can be calculated using the formula:
Weight = mass * gravity
where gravity is approximately 9.8 m/s².

Weight = 400 kg * 9.8 m/s²
Weight = 3920 N

5. Determining the coefficient of friction:
The coefficient of friction (μ) is the ratio of the force of friction to the normal force:
μ = F / N
where F is the force of friction and N is the normal force.

Substituting the calculated values:
μ = 2940 N / 3920 N
μ ≈ 0.75

6. Conclusion:
The coefficient of friction between the tires of the car and the surface it travels on is approximately 0.75. This coefficient indicates the amount of friction between the two surfaces and can be used to determine the car's ability to grip the road and stop efficiently.