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  4. 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 :

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Q. 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 :

JEE MainJEE Main 2022Mechanical Properties of Fluids

Solution:

$ V ^{2}=2 \times 9.8 \times 4.9 $
$ V =9.8\, m / s$
Depth $=$ distance travelled in $3$ seconds
$=9.8 \times 3=29.4\, m$