A bullet is fired at a plank of wood with a speed of 200m/s. After passing through the plank, its speed reduces to 180m/s. Another bullet, of the same mass and size but moving with a speed of 100m/s is fired at the same plank. What would be the speed of this bullet after passing through the plank?? Assume that the resistance offered by the plank is the same for both the bullets.

let the retardation is constant(a) then we can use

v² = u² +  2as

v²-u² = 2as                         ( s is width of plank)

for first bullet , v = 180 , u = 200

180² - 220² = 2as      ...............1

for second bullet , v=? , u = 100 so

v² - 100² = 2as          ..............2              (width of plank & resistance remains same)

divide 1/2

180² - 200²/v²-100² = 1

v² = 2400

v = 49m/s

Approved

thnku