Question

Draw a free body diagram and apply newtons second law

Why does an ordinary rifle recoil (kick backward) when fired? The barrel of a recoilless rifle is open at both ends. Describe how Newton’s third law applies when one is fired.

Answer 1

Newton's second law

F = m*a

a = F/m

so

The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.

Why does an ordinary rifle recoil

this can be explained by newtons third law

Newton's third law is: For every action, there is an equal and opposite reaction

here is action is firing and reaction is recoil  

in rifle barrel gunpowder exert force on bullet in forward direction and in return bullet apply same magnitude reaction force on rifle in backward so we feel recoil after firing a rifle

recoilless rifle is open

but it is open on both side so we can't fire bullet with this so no recoil force here

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