From a rifle of mass 4 kg, a bullet of mass 50 g is fired with an initial velocity of 35 m s-1 . Calculate the initial recoil velocity of the rifle.

Answers (1)

Here we will use conservation of momentum : 

                                   Initial momentum of system ( rifle + bullet )    =   Final momentum of system

                                                                       m_1u_1\ +\ m_2u_2\ =\ m_1v_1\ +\ m_2v_2

or                                                              4\times 0\ +\ 0.05\times 0\ =\ 4\times v_1\ +\ 0.05\times 35

or                                                                                   -4 \times v_1\ =\ 1.75

or                                                                                               v_1 \ =\ -\ 0.4375\ m/s

The negative sign shows that velocity is opposite to that of the bullet. This is because the force on the rifle will be opposite by bullet (action-reaction pair).

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