Question

An open water tight railway wagon of mass $5\times {10}^{3}kg$ coasts at an initial velocity of $1.2m/s$ without friction on a railway track. Rain falls vertically downwards into the wagon. What change then occurred in the kinetic energy of the wagon, when it has collected ${10}^3$ kg of water ?

• A. 1200 J
• B. 300 J
• C. 600 J
• D. 900 J

Answer 1

Answer: (C)

600 J

From COCM
$5\times {10}^3\times 1.2=6\times {10}^3{V}^{\prime }$
$V^{\prime }=1m/s$
$\Delta KE=\frac{1}{2}m{v}^2-\frac{1}{2}{m}^{\prime }{v}^{\prime 2}$
$=\frac{1}{2}\times 5\times {10}^3\times (1.2{)}^2-\frac{1}{2}\times 6\times {10}^3(1{)}^2$
$=600J$