Question

If a body is dropped freely from a height of 80 m, then the time taken by the body to reach the ground is (g =10m/s)​

Answer 1

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• 2.4 second

Answer 2

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Let the value of coefficient of restitution be e.

Initial height of the body H=80 m

$Time\: taken \: by \: the \: body \: to \: reach \: the \: ground \: t \: = \sqrt{ \frac{211}{g} }$

$t = \sqrt{ \frac{2 \times 80}{10} } = 4 \: s$

$Total \: time \: taken \: by \: body \: to \: stop \: is \: given \: by \: t \: = t ( \frac{1 + e}{1 - e} )$

$6 = 4( \frac{1 + e}{1 - e} )$

$e = 0.2$

Total distance travelled by body before coming to rest is given by S =

$h( \frac{1 + {e}^{2} }{1 - {e}^{2} } )$

$s = 80( \frac{1 + {0.2}^{2} }{1 - 0.2} ) = 86.6 m$