A bullet of mass 200g having initial kinetic energy 90 J is shot inside a long swimming pool as shown in the figure. If it’s kinetic energy reduces to 40 J within 1s, the minimum length of the pool, the bullet has to travel so that it completely comes to rest is

<p>m = 200 g, ki = 90 J kf = 40 J., &nbsp;<math><mrow><mi>Δ</mi><mi>t</mi><mo>=</mo><mn>1</mn><mi>s</mi><mi>e</mi><mi>c</mi></mrow></math></p><p><math><mrow><mo>⇒</mo><mi>F</mi><mo>=</mo><mfrac><mrow><msub><mrow><mi>k</mi></mrow><mrow><mi>f</mi></mrow></msub><mo>−</mo><msub><mrow><mi>k</mi></mrow><mrow><mi>i</mi></mrow></msub></mrow><mrow><mi>x</mi></mrow></mfrac><mo>⇒</mo><mroot><mrow><mo>.</mo><mn>4</mn><mo>×</mo><mn>9</mn><mn>0</mn></mrow><mrow></mrow></mroot><mo>−</mo><mroot><mrow><mo>.</mo><mn>4</mn><mo>×</mo><mn>4</mn><mn>0</mn></mrow><mrow></mrow></mroot><mo>=</mo><mi>F</mi><mo>×</mo><mn>1</mn></mrow></math></p><p><math><mrow><mo>⇒</mo><mi>F</mi><mo>=</mo><mn>6</mn><mo>−</mo><mn>4</mn><mo>=</mo><mn>2</mn><mi>N</mi></mrow></math></p><p>So for complete rest :-</p><p>Fx = 90 J</p><p>2x = 90 x = 45 m</p>

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