Question

Greater is the range, longer should be length of barrel of a gun. What is the reason behind this belief?

• A. To allow better cooling of the gun due to increased surface area.
• B. To allow the force of the expanding gases to act for a longer distance.
• C. To increase the force exerted on the shell due to the expanding gases.
• D. To provide a more favourable ratio of kinetic energy to potential energy.

Answer 1

Answer: (B)

(b)

Answer 2

The primary reason why a longer barrel is associated with a greater range for a gun is related to the physics of projectile motion and the work done on the projectile inside the barrel.

When a gun is fired, the gunpowder explodes, producing a large volume of rapidly expanding hot gases. These gases exert pressure on the base of the projectile (bullet or shell), pushing it forward along the barrel.

According to the work-energy theorem, the work done on an object is equal to the change in its kinetic energy.

$W = F \times d$

In a gun barrel, the force exerted by the expanding gases acts on the projectile as it travels down the barrel. If the barrel is longer, the expanding gases have a greater distance over which to act on the projectile. This means more work is done on the projectile by the expanding gases. More work done translates to a greater increase in the projectile's kinetic energy when it leaves the barrel. A higher kinetic energy at the muzzle means a higher muzzle velocity. A higher muzzle velocity is directly correlated with a greater range, assuming the launch angle is optimal.