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1
A rifle with a weight of 25 N fires a 3.5 g bullet with a speed of 280 m/s.

(a) Find the recoil speed of the rifle.
m/s

(b) If a 725 N man holds the rifle firmly against his shoulder, find the recoil speed of the man and rifle.
m/s
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Added Mon, 03 Aug '15
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This is a question about the conservation of momentum and Netwon's third law, every action has an equal and opposite reaction.

Let, m = 0.0035 kg - the mass of the bullet
v = 280 m/s

M = 25/9.8 = approx 2.5 kg
V =?

By the conservation of momentum,
mv = MV, therefore V = mv/M

V=0.0035x280 / 2.5 = 0.392 m/s in the opposite direction to the bullet.

b) Same thing but sum the man+rifle for M.=2.5+72.5=75

V=0.0035x280 / 75= 0.0130 m/s in the opposite direction to the bullet.
Edit
Added Mon, 03 Aug '15
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