Question

The velocity of bullet is reduced from $200\, m / s$ to $100 \,m / s$ while travelling through a wooden block of thickness of $10 \,cm$. The retardation assuming to be uniform, will be :

• A. $15 \times 10^{4}\, m / s ^{2}$
• B. $13.5 \times 10^{4} \,m / s ^{2}$
• C. $12 \times 10^{4} \,m / s ^{2}$
• D. none of these

Answer 1

Answer: (A)

$15 \times 10^{4}\, m / s ^{2}$

Answer 2

Here: initial velocity $=200\, m / s$ Final velocity $(v)=100\, m / s$ distance $s=10 \,cm =0.1 \,m$ Using the-relation of equation of motion $v^{2}=u^{2}+2\, a s$ $a=\frac{v^{2}-u^{2}}{2 s}=\frac{(100)^{2}-(200)^{2}}{2 \times 0.1}$ $=\frac{10000-40000}{2 \times 0.1}=\frac{\frac{-300000}{2}}{2}$ $=-150000\, m / s ^{2}=-15 \times 10^{4} \,m / s ^{2}$ $(-)$ minus sign denotes retardation