Answer
(a) decrease
(b) $0.349$
Work Step by Step
(a) We should decrease the coefficient of kinetic friction so that the system can have more kinetic energy and a larger final speed than $1.30m/s.$
(b) We can find the required coefficient of kinetic friction as follows:
$\mu_k=\frac{m_2gd-(\frac{1}{2})(m_1+m_2)v_f^2}{m_1gd}$
We plug in the known values to obtain:
$\mu_k=\frac{(1.80)(9.81)(0.500)-(\frac{1}{2})(4.20)(1.50)^2}{(2.40)(9.81)(0.500)}$
$\mu_k=0.349$
