When a ball is dropped into a lake from a height 4.9 ,m above water level, it hits water with a velo

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2.Motion in Straight Line

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When a ball is dropped into a lake from a height $4.9 \,m$ above the water level, it hits the water with a velocity $v$ and then sinks to the bottom with the constant velocity $v$. It reaches the bottom of the lake $4.0,s$ after it is dropped. The approximate depth of the lake is ............ $m$

A

$19.6$

B

$29.4$

C

$39.2$

D

$73.5$

(JEE MAIN-2022)

Solution

$V ^{2}=2 \times 9.8 \times 4.9$

$V =9.8 \,m / s$

Depth $=$ distance travelled in $3$ seconds

$=9.8 \times 3=29.4 \,m$

Standard 11

Physics

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