A bullet fired into a fixed target loses 20% of its K.E.in penetrating 1 cm. Find the total distance penetrated by bullet before it comes to rest :

Options

A. 2 cm
B. 3 cm
C. 4 cm
D. 5 cm

Answer

d

Explanation

Here `1/2mv^2=(1-(20)/(100))xx1/2"mu"^2`
or `v^2=4/5u^2`
Applying `v^2-u^2=2aS,4//5u^2=u^2-2axx1` or `a=(u^2)/(10)`.
Let .x. be the distance penetrated.When bullet comes to rest i.e v=0, then `:. 0=u^2-2(u^2/10)x`
or x=5 cm.