Question

A bullet of mass $15$ g has a speed of $400m/s$. What is its kinetic energy? If the bullet strikes at target brought to rest in $2$ cm. Calculate the average net force acting on the bullet. What happens to the kinetic energy originally in the bullet ?

Answer 1

Given,

Mass$\left(M\right)=15$gm $=15\times {10}^{-3}$kg

Initial velocity$=400$m/s

Distance travelled(s)$=2$cm$=2\times {10}^{-2}$m

(i) Kinetic energy$=\frac{1}{2}m{v}^2$

$=\frac{1}{2}\times 15\times {10}^{-3}\times (400{)}^2$

$=\frac{1}{2}\times 15\times {10}^{-3+4}\times 16$

$=1200J$

(ii) The bullet strikes a thick target and is broght to rest in $2$cm

work done$=$change in K.E

[$v_f=0$ final velocity]

$F.S=1200J-0$

$F=\frac{1200N}{2\times {10}^{-2}}$

$F=6\times {10}^{4}N$

(iii) The Kinetic energy is converted to heat & sound energy.