Question

8.
A bullet travelling horizontally looses 1/20th
of its velocity while piercing a wooden plank.
Then the number of such planks required to
stop the bullet is
1) 6 2) 9 3) 11
4) 13​

Answer 1

Answer:

3) 11

Explanation:

If the bullet looses 1/20th of its velocity then

V= 19/20u

Since, v² = u² + 2as

(19/20u)² = u² - 2as

2as = u² - (19/20u)² ................(1)

Now, initial velocity = 0

Therefore 0² = u² - 2a (ns)

u² = 2as (n)

u² = n [ u² - 19²/20² u²]

u² = nu² [ 20²-19²/20²]

20² = n [ 20² - 19² ]

20² = n [ (20+19)(20-19) ]

n = 400/39

n ~ 11 planks