The coefficient of kinetic friction between block $A$ of mass 5 kg and the table is 0.3. What would

Question

The coefficient of kinetic friction between block $A$ of mass 5 kg and the table is 0.3. What would be the mass of the hanging block $B$ so that the two blocks move with uniform speeds once set into motion? The string and the pulley are assumed to be smooth and massless. ( $g=10 \mathrm{~m} / \mathrm{s}^{2}$ )

Professor PC Thomas Classes · Answer

For uniform speed, acceleration $a = 0$. The tension $T$ must balance the friction on $A$ and the weight of $B$. $T = m_B g$ and $T = \mu_k m_A g$. Therefore, $m_B g = \mu_k m_A g \implies m_B = \mu_k m_A = 0.3 	imes 5 = 1.5 \mathrm{~kg}$.