Question

A bullet is fired at a plank of wood with a speed of 200ms. After passing through the plank. its speed
reduces to 180ms. If the mass of the bulletis 10g and the thickness of wooden plank is in the avenge
resistance offered by the plank is

a) 36 N
b) 38 N
c) 40 N
d) 42 N

plz answer if u know only​

Answer 1

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