b
રેખીય વેગમાં સરક્ષણ નાં નિયમ પરથી, \(\,{\text{2}}\,\, \times \,\,{\text{1}}{\text{.5}}\,\, + \;\,{\text{3}}\,\, \times \,\,{\text{0}}\,\, = \,\,{\text{2}}\,\,{{\text{V}}_{\text{1}}}\,\, + \;\;3\,\, \times \,\,1\,\, \Rightarrow \,\,{V_1}\,\, = \,\,0\)

\(K{E_1}\,\, = \,\,\frac{1}{2}\,\, \times \,\,2\,\, \times \,\,{\left( {1.5} \right)^2}\,\, = \,\,2.25\,\,J\,\,\, \)

\(\Rightarrow \,\,K{E_1}\,\, = \,\,\frac{1}{2}\, \times \,\,3\,\, \times \,\,{1^2}\,\, = \,\,1.5\,\,J\,\,\,\therefore \,\,\,\Delta \,KE\,\, = \,\,0.75\,J\)