A particularly eccentric member of a gun enthusiast club has developed a rifle t

Question

A particularly eccentric member of a gun enthusiast club has developed a rifle that fires a bullet which is ten times as massive as the rifle from which it is fired. He stands on a platform with the gun pointed down a shooting range and, against the wishes of his physics-knowing colleagues. If the rifle weighs 7.7 kg and the bullet leaves the muzzle with a velocity of 50 m/s, with what velocity is the 86.0 kg man launched backwards, assuming his arm stays intact and he manages to hang on to the rifle?

Explanation / Answer

given
m_rifile = 7.7 kg

m_bullet = 10*7.7 = 77 kg

m_man = 86 kg

now Apply conservation of energy

momentum gained by man and rifle backward = momentum gained by bullet in forward direction

(7.7 + 86)*v = 77*50

v = 77*50/(7.7 + 86)

= 41 m/s

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