Question

A body falls freely from rest .it covers as much distancrin the last second of its motion as covered in the first three second .the bodu

Answer 1

ok wait i will help you

Answer 2

if. Que... is A stone is falling freely from the rest and the total distance covered by it in the last second of its motion equals the distance covered by it in the first 3 seconds of its motion .How long does the stone remain in air ?

$\fcolorbox{red}{white}{solution : - } \\ \\ \underline{ \red{we \: know \: the \: acceleration \: due \: to \:}} \\ \underline{ \red{gravity \: is \: }9.8 \: m/ {s}^{2} \:\ \red{ but \: we \: take \: }10 \: m/ {s}^{2} } \\ \\\underline{ \red {now \: }} \\ \underline{to \: calculate \: distance \: travel \: by \: stone} \\ \underline{ we \: use}\\ \mathfrak{ \red{formula : - }} \\ \\ s = ut + \frac{1}{2} a {t}^{2} \\ \\ \underline \red{where} \\ \\ {\red{v \:} = \: final \: velocity \: } \\ {\red{u \: } = \: initial \: velocity \: } \\ {\red{a \:} = \: acceleration} \\ {\red{t \:} = \: time \: taken} \\ \\ \underline \red{we \: know \: initial \: velocity \: is \: 0} \ \\ \underline{ hence} \\ \\ \\ s = \frac{1}{2} \times 10 \times {3}^{2} \\ \\ s \: = \frac{1}{2} \times 10 \times 9 \\ \\ s = \frac{90}{2} = 45 \: units \\ \\ \underline{\fbox{to \: find}} \\ \\ \underline{ \: How \: long \: does \: the \: stone \: remain \: in \: air ... } \\ \\\underline{ \red{ we \: use}} \\ \\ s = \frac{u + a}{2} \times (2n - 1) \\ \\ we \: know \: \red { u = 0 } \: and \: \: \red{ a = 10} \: and \: \red{ s = 45 \: units} \: \\ so \\ \\ 45 = \frac{0 + 10}{2} \times ( 2n - 1) \\ \\ \\ 45 = 5(2n - 1) \\ i.e. \\ \\ 5(2n - 1) = 45 \\ \\ 2n - 1 = \frac{45}{5} \\ \\ 2n - 1 = 9 \\ \\ 2n = 9 + 1 \\ \\ 2n = 10 \\ \\ n \: = \frac{10}{2} \\ \\ \fcolorbox{red}{white}{ n \: = 5 \: sec} \\ \\ \underline{ so \: we \: know \: now \: } \\ \\ \small{\fcolorbox{red}{white}{The \: stone \: remains \: in \: the \: air \: for \: 5 \: sec}} \\ \\ \underline\red{i \: hope \: it \: helps \: you}.....$