Question

A bullet of mass 5g is fired from a gun with a velocity of 100ms-¹. What is its K.E.? If the barrel of the gun is 80cm long, what force is acted on the bullet by the burnt gas?

Force, Energy and Power (Class X ICSE)​

Answer 1

Answer:

Mass of bullet, m=100g=

1000

100

kg=

10

1

kg

Velocity of bullet, v=100ms

−1

Mass of gun, M=20kg

Let recoil velocity of gun =V

Before firing, the system (gun+bullet) is at rest, therefore, initial momentum of the system =0

Final momentum of the system = momentum of bullet + momentum of gun

=mv+MV=

10

1

×100+20V=10+20V

Applying law of conservation of momentum, Final momentum = Initial momentum

i.e., 10+20V=0

20V=−10

or V=−

20

10

=−0.5ms

−1

.

Negative sign shows that the direction of recoil velocity of the gun is opposite to the direction of the velocity of the bullet.