Physics

Problem

Block

A

of mass

4\,\text{kg}

rests on a horizontal table and is connected by a light string over a frictionless pulley to a hanging block

B

(mass

m_B

). The coefficient of static friction between block

A

and the table is

\mu_s=0.50

. What is the minimum mass

m_B

that will cause block

A

to start moving? (Take

g=9.8\,\text{m/s}^2

.) a)

8.0\,\text{kg}

1.0\,\text{kg}

2.0\,\text{kg}

4.0\,\text{kg}

Intuitive explanation

This is about finding the threshold where tension overcomes static friction. Block $B$ 's weight creates tension in the string, which pulls block $A$ horizontally—but $A$ won't budge until that tension exceeds the maximum static friction force holding it in place. Set up the friction limit ( $\mu_s$ times the normal force on $A$ ) and equate it to the tension needed to move the system, then solve for $m_B$ .

Intuitive explanation

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