A bullet of 10 g is fired with a velocity of 1200 m/s and strikes a wall with a velocity of 400 m/s. The loss in energy while overcoming the resistance of air is-

The correct answer is option 3) i.e. 6400 J

CONCEPT:

• Work-energy theorem: The work-energy theorem states that the net work done by the forces on an object equals the change in its kinetic energy.

​Work done, \(W = Δ KE = \frac{1}{2}mv^2 - \frac{1}{2}mu^2\)

Where m is the mass of the object, v is the final velocity of the object and u is the initial velocity of the object. 

CALCULATION:

Given that:

Mass, m = 10 g = 0.01 kg

Initial velocity, u = 1200 m/s

Final velocity, v = 400 m/s

The loss in energy = Work done

\(⇒ Δ KE = W\)

\(⇒​​​​ W=\frac{1}{2}m(v^2 -u^2)\)

\(⇒ ​​​​W=\frac{1}{2}\times 0.01\times(1200^2 -400^2)\)

⇒ W = 6400 J