Verified Solution • 2025–26 Session moderate

QJEEM22Pha342: JEE Main 2022 Physics - Class 11 JEEM22Pha342 Solution: When a ball is dropped into a lake from a height 4.9 m above…

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 :

Multiple Choice Options

  • A 19.6 m
  • B 29.4 m
  • C 39.2 m
  • D 73.5 m

Step-by-Step Verified Solution

t1=2hg{t_1} = \sqrt {{{2h} \over g}}

=2×4.99.8=1 s= \sqrt {{{2 \times 4.9} \over {9.8}}} = 1\,s

Δt=4−1=3 s\Delta t = 4 - 1 = 3\,s ,

v=2gh=2×9.8×4.9=9.8v = \sqrt {2gh} = \sqrt {2 \times 9.8 \times 4.9} = 9.8 m/s

∴\therefore depth =9.8×3=29.4= 9.8 \times 3 = 29.4 m

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