9th Class Science Force and laws of motion Question Bank 9th CBSE Science Force and laws of motion

  • question_answer
    A bullet of mass 0.02 kg is fired from a gun weighing 7.5 kg. If the initial velocity of the bullet is 200 m/s, calculate the speed with which the gun recoils.

    Answer:

                                                                            Here, the mass of the bullet, \[{{m}_{1}}=0.02kg\] Mass of gun,     \[{{m}_{2}}=75kg\] Velocity of bullet, \[{{\upsilon }_{1}}=200m/s\]and the speed of gun, \[{{\upsilon }_{2}}=?\]                                                       According to law of conservation of momentum, Total momentum of system after firing = Total momentum of system before firing i.e.,  \[{{m}_{1}}{{\upsilon }_{1}}+{{m}_{2}}{{\upsilon }_{2}}=0\]                (Since initial velocities of gun and bullet before firing is zero.) or \[0.02\times 200+7.5\times {{\upsilon }_{2}}=0\] or \[7.5\times {{\upsilon }_{2}}=-0.02\times 200\] or \[{{\upsilon }_{2}}=-\frac{4}{7.5}=-0.533\] or  \[{{\upsilon }_{2}}=-0.53m/s\]


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