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QJEEM23Phae2b: JEE Main 2023 Physics - Class 11 JEEM23Phae2b Solution: A bullet of leaves the barrel of gun with a velocity of . If…

A bullet of 10 g10 \mathrm{~g} leaves the barrel of gun with a velocity of 600 m/s600 \mathrm{~m} / \mathrm{s} . If the barrel of gun is 50 cm50 \mathrm{~cm} long and mass of gun is 3 kg3 \mathrm{~kg} , then value of impulse supplied to the gun will be :

Multiple Choice Options

  • A 12 Ns
  • B 3 Ns
  • C 6 Ns
  • D 36 Ns

Step-by-Step Verified Solution

First, we need to find the velocity of the gun after the bullet is fired. We can use conservation of momentum to do this. The total momentum of the system of the gun and bullet is conserved before and after the bullet is fired. Therefore, we can write

mgug+mbub=mgvg+mbvbm_g u_g + m_b u_b = m_g v_g + m_b v_b

where ug=0u_g = 0 is the initial velocity of the gun, ub=600 m/su_b = 600 \mathrm{~m/s} is the initial velocity of the bullet, mg=3 kgm_g = 3 \mathrm{~kg} is the mass of the gun, mb=0.01 kgm_b = 0.01 \mathrm{~kg} is the mass of the bullet, vb=0v_b = 0 is the final velocity of the bullet (since it has left the gun), and vgv_g is the final velocity of the gun.

Substituting the given values, we get

(3 kg)(0)+(0.01 kg)(600 m/s)=(3 kg)vg+(0.01 kg)(0)(3 \mathrm{~kg})(0) + (0.01 \mathrm{~kg})(600 \mathrm{~m/s}) = (3 \mathrm{~kg})v_g + (0.01 \mathrm{~kg})(0)

Solving for vgv_g , we get

vg=0.01 kg×600 m/s3 kg=2 m/sv_g = \frac{0.01 \mathrm{~kg} \times 600 \mathrm{~m/s}}{3 \mathrm{~kg}} = 2 \mathrm{~m/s}

Therefore, the velocity of the gun after the bullet is fired is vg=2 m/sv_g = 2 \mathrm{~m/s} .

Next, we need to find the impulse on the gun. The impulse-momentum theorem states that the impulse on an object is equal to the change in momentum of that object. Therefore, the impulse on the gun is given by

I=Δp=mgΔvI = \Delta p = m_g \Delta v

where Δv=vf−ug\Delta v = v_f - u_g is the change in velocity of the gun. Since the initial velocity of the gun is zero, we can write Δv=vg\Delta v = v_g .

Substituting the given values, we get

I=(3 kg)×(2 m/s)=6 NsI = (3 \mathrm{~kg}) \times (2 \mathrm{~m/s}) = 6 \mathrm{~Ns}

Therefore, the impulse on the gun is 6 Ns6 \mathrm{~Ns} , which is the correct answer.

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