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# A ball of mass 4kg, moving with a velocity of

Question:

A ball of mass $4 \mathrm{~kg}$, moving with a velocity of $10 \mathrm{~ms}^{-1}$, collides with a spring of length $8 \mathrm{~m}$ and force constant $100 \mathrm{Nm}^{-1}$. The length of the compressed spring is $x \mathrm{~m}$. The value of $x$, to the nearest integer, is______.

Solution:

Let's say the compression in the spring by : y. So, by work energy theorem we have

$\Rightarrow \frac{1}{2} \mathrm{mv}=\frac{1}{2} \mathrm{ky}^{2}$

$\Rightarrow y=\sqrt{\frac{m}{k}} \cdot v$

$\Rightarrow y=\sqrt{\frac{4}{100}} \times 10$

$\Rightarrow y=2 m$

$\Rightarrow$ final length of spring

$=8-2=6 m$