Q: If the block on the bench is $$4.0\ \mathrm{kg}$$ and the hanging mass is $$2.4\ \mathrm{kg}$$, what is the tension in the string when the system is at rest?

$$2.4 \times 9.8 = 23.5\ \mathrm{N}$$

Question 1

Three objects are connected by weightless flexible strings as shown in the figure. The pulley has no appreciable mass or friction, and the string connected to the block on the horizontal bench pulls on it parallel to the bench surface. The coefficients of friction between the bench and the block on it are $$\mu_s = 0.60$$ and $$\mu_k = 0.325. $$The system remains at rest. If the mass of the block on the bench is $$4.0\ \mathrm{kg}$$, what is the minimum mass of the hanging object $$A$$ that will just start to move the system?

Accepted Answer

$$2.4\ \mathrm{kg}$$

Question 2

Given the system in the figure, if the coefficient of kinetic friction $$\mu_k is$$ $$0.325$$, what is the magnitude of the friction force acting on the block on the bench when the system is moving?

Accepted Answer

$$12.7\ \mathrm{N}$$

Question 3

If the system described is at rest, which of the following correctly describes the relationship between the tension $$T in $$the string and the friction force $$f on $$the block on the bench?

Accepted Answer

$$T = f$$

Question 4

Suppose the mass of the hanging object $$A is $$increased slightly above the minimum value required to start motion. What will happen to the friction force acting on the block on the bench?

Accepted Answer

It will decrease to the kinetic friction value.

Question 5

If the coefficient of static friction $$\mu_s is$$ $$0.60$$ and the block on the bench has mass $$4.0\ \mathrm{kg}$$, what is the maximum static friction force that can act on the block?

Accepted Answer

$$23.5\ \mathrm{N}$$

Question 6

If the system is at rest, what is the value of the tension in the string connecting the block on the bench to the hanging mass?

Accepted Answer

$$T = m_A g$$

Question 7

If the block on the bench has mass $$m_B$$ and the hanging mass is $$m_A$$, which equation correctly represents the condition for the system to just start moving?

Accepted Answer

$$m_A g = \mu_s m_B g$$

Question 8

If the block on the bench is $$4.0\ \mathrm{kg}$$ and the acceleration due to gravity is $$9.8\ \mathrm{m/s^2$}$$, what is the normal force acting on the block?

Accepted Answer

$$39.2\ \mathrm{N}$$

Question 9

If the system is moving at constant velocity, what is the net force acting on the block on the bench?

Accepted Answer

$$0\ \mathrm{N}$$

Question 10

If the coefficient of kinetic friction is $$\mu_k = 0.325$$ and the block on the bench has mass $$4.0\ \mathrm{kg}$$, what is the acceleration of the block if the hanging mass is $$3.0\ \mathrm{kg}$$? (Assume $$g = 9.8\ \mathrm{m/s^2$}$$ and neglect the mass of the pulley and string.)

Accepted Answer

$$a = \dfrac{m_A g - \mu_k m_B g}{m_A + m_B}$$

Question 11

If the system is at rest, which force is responsible for preventing the block on the bench from moving?

Accepted Answer

Static friction

Question 12

If the coefficient of static friction is $$\mu_s = 0.60$$, what is the physical meaning of this value in the context of the experiment?

Accepted Answer

It is the ratio of the maximum static friction force to the normal force.

Question 13

If the block on the bench is $$4.0\ \mathrm{kg}$$ and the coefficient of kinetic friction is $$0.325$$, what is the work done by friction when the block moves $$2.0\ \mathrm{m}$$?

Accepted Answer

$$25.4\ \mathrm{J}$$

Question 14

If the system is at rest and the tension in the string is less than the maximum static friction force, what will happen?

Accepted Answer

The block will not move.

Question 15

If the block on the bench is $$4.0\ \mathrm{kg}$$ and the hanging mass is $$2.4\ \mathrm{kg}$$, what is the tension in the string when the system is at rest?

Accepted Answer

$$2.4 	imes 9.8 = 23.5\ \mathrm{N}$$

Static Equilibrium and Friction: Pulley System Analysis

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