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5.Work, Energy, Power and Collision
medium
A ball of mass $4\, kg$, moving with a velocity of $10\, ms ^{-1}$, collides with a spring of length $8\, m$ and force constant $100\, Nm ^{-1}$. The length of the compressed spring is $x\, m$. The value of $x$, to the nearest integer, is ........ .
A
$4$
B
$9$
C
$6$
D
$12$
(JEE MAIN-2021)
Solution
Let's say the compression in the spring by: $y$.
So, by work energy theorem we have
$\Rightarrow \frac{1}{2} mv ^{2}=\frac{1}{2} ky ^{2}$
$\Rightarrow y =\sqrt{\frac{ m }{ k }} \cdot v$
$\Rightarrow y=\sqrt{\frac{4}{100}} \times 10$
$\Rightarrow y =2\, m$
$\Rightarrow$ final length of spring $=8-2=6\, m$
Standard 11
Physics