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3. If you use a horizontal force of 30.0 N to slide a 12.0-kg wooden crate across a floor at a constant velocity, what is the coefficient of kinetic friction between the crate and the floor?

4. A force of 4.0N is large enough to overcome the friction between a 5.0-kg block and a horizontal surface and accelerate the block at 6.0m/s2

A. How large is the friction force?

B. What is the coefficient of friction?

To answer the questions, we need to understand the concepts of friction and the coefficient of friction. The coefficient of kinetic friction measures the resistance between two surfaces when they are in motion relative to each other. The formula to calculate the force of friction is:

Friction force = coefficient of friction * normal force

1. To find the coefficient of kinetic friction in question 3, we need to examine the forces acting on the crate. Since the crate is moving at a constant velocity, we know that the net force on it is zero. Therefore, the force of friction must be equal in magnitude and opposite in direction to the applied force.

2. The force of friction can be calculated by multiplying the coefficient of kinetic friction by the normal force (which is the force exerted by the surface on the crate perpendicular to the surface). In this case, the normal force is equal to the weight of the crate (mass * acceleration due to gravity).

3. Since the crate is not accelerating, we know that the applied force is equal in magnitude and opposite in direction to the force of friction. Therefore, the force of friction is 30.0 N.

4. To find the coefficient of friction, we can rearrange the formula for friction force and solve for the coefficient:

coefficient of friction = force of friction / normal force

5. The normal force in this case is equal to the weight of the block (mass * acceleration due to gravity).

By using the given values and following these steps, we can find the answers to questions 3 and 4.

3. net force=ma

applied force-frictionforce=ma
so if a is zero, then friction force=?
4. appied force-frictionforce=ma
solve for friction force.