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5.Work, Energy, Power and Collision
hard
A bullet of mass $50 \mathrm{~g}$ is fired with a speed $100 \mathrm{~m} / \mathrm{s}$ on a plywood and emerges with $40 \mathrm{~m} / \mathrm{s}$. The percentage loss of kinetic energy is :
A
$32 \%$
B
$44 \%$
C
$16 \%$
D
$84 \%$
(JEE MAIN-2024)
Solution
$\mathrm{K}_{\mathrm{i}} =\frac{1}{2} \mathrm{~m}(100)^2$
$\mathrm{~K}_{\mathrm{f}} =\frac{1}{2} \mathrm{~m}(40)^2$
$\% \text { loss }=\frac{\left|\mathrm{K}_{\mathrm{f}}-\mathrm{K}_{\mathrm{i}}\right|}{\mathrm{K}_{\mathrm{i}}} \times 100$
$=\frac{\left|\frac{1}{2} \mathrm{~m}(40)^2-\frac{1}{2} \mathrm{~m}(100)^2\right|}{\frac{1}{2} \mathrm{~m}(100)^2} \times 100$
$=\frac{|1600-100 \times 100|}{100}=84 \%$
Standard 11
Physics
