Question

A rifle bullet loses 1/20th of its velocity in passing through a plank. The least number of such planks required just to stop the bullet is

Answer 1

⛦Hҽɾҽ ɿʂ ү๏υɾ Aɳʂฬҽɾ⚑
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➧ No. of planks
➾ n² / 2n - 1

➧ Where n is loss in velocity.

➧ There your answer will not consume time as time is marks in such exam,

➾ 20² / 2 × 20 - 1
➾ 10.25
➾ 11 planks ...✔

_________
Thanks...✊

Answer 2

☆ No. of planks = n2 / 2n - 1

☆ Where n is loss in velocity

☆ There your answer will not consume time as time is mark I'm such exam

☆ 20×20 / 2 × 20-1
☆ 10.25
☆ 11 planks

HOPE IT WILL HELP YOU