A bullet of mass 0.01 kg is fired from a gun of mass 5 kg. If the bullet leaves the gun with a velocity of 500 m/s, what is the recoil velocity of the gun?
Correct: B
According to the Law of Conservation of Momentum, the total momentum before firing (0) equals the total momentum after firing. Let m_b = 0.01 kg (mass of bullet), v_b = 500 m/s (velocity of bullet), m_g = 5 kg (mass of gun), v_g = recoil velocity of gun. So, 0 = (m_b × v_b) + (m_g × v_g). 0 = (0.01 kg × 500 m/s) + (5 kg × v_g). 0 = 5 kg m/s + 5 kg × v_g. 5 kg × v_g = -5 kg m/s. v_g = -5/5 = -1 m/s. The negative sign indicates the recoil is in the opposite direction to the bullet's motion.