Question

a rifle can shoot a 4.20g bullet at a speed of 965m/s

what is the kinetic energy of the bullet

Answer 1

By definition, the kinetic energy is:

$$K = \dfrac{mv^2}{2}$$

where $m = 4.20g = 4.2\times 10^{-3}kg$ is the mass of the bullet, and $v = 965 m/s$ is its speed. Thus, obtain:

$$K = \dfrac{4.2\times 10^{-3}\cdot 965^2}{2} \approx 1.96\times 10^{6}J$$

Answer. $1.96\times 10^{6}J$.