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Question Number 68278 by TawaTawa last updated on 08/Sep/19

Commented by mr W last updated on 08/Sep/19

$i t i s t o s e e t h a t t h e c r o c o d i l e t a k e s$ $0.5 s e c o n d s f o r 1 m e t e r i n w a t e r a n d$ $0.4 s e c o n d s f o r 1 m e t e r o n l a n d . i s$ $t h i s t r u e ? b e c a u s e i t h o u g h t a c r o c o d i l e$ $i s f a s t e r i n w a t e r t h a n o n l a n d . . . .$ ${l e t}^{'} s a s s u m e t h e b o o k i s r i g h t .$ $(a) (i)$ $w i t h x = 20, T = 5 \sqrt{36 + 400} = 104 = 10.4 s e c$ $(a) (i i)$ $w i t h x = 0, T = 5 \sqrt{36} + 4 \times 20 = 110 = 11 s e c$ $(b)$ $\frac{d T}{d x} = \frac{5 x}{\sqrt{36 + x^{2}}} - 4 = 0$ $25 x^{2} = 16 (36 + x^{2})$ $x^{2} = 64$ $\Rightarrow x = 8$ $T_{m i n} = 5 \sqrt{36 + 64} + 4 \times 12 = 98 = 9.8 s e c$
Commented by TawaTawa last updated on 08/Sep/19

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