Law of Conservation of Momentum

Why does a gun recoil backward when fired? Explain.

A railway wagon of mass $\frac{1}{2 } \mathrm{ton}$ moving with a velocity of $10 \mathrm{km}/\mathrm{h}$, is hit from behind by another railway wagon of mass  $1\frac{1}{2} \mathrm{ton}$ moving at $15 \mathrm{km}/\mathrm{h}$, such that after the collision, they move together. Calculate the final velocity of the wagons.

A bullet of mass $15 \mathrm{g}$ and moving with a velocity of $300 \mathrm{ms}{ }^{-1}$ gets embedded in a freely suspended wooden target of mass $735 \mathrm{g}$. Calculate the velocity of the target on being hit.

A pistol of mass $0.75 \mathrm{kg}$ recoils with a velocity of $0.25 \mathrm{m}/\mathrm{s}$. If the bullet leaves the shell with a velocity of $80 \mathrm{m}/\mathrm{s}$ find the mass of the bullet.

 A gun of mass $\frac{1}{2 }$ ton  recoils with a velocity of  $0.8 \mathrm{m}/\mathrm{s}$, while firing a shell of mass $4 \mathrm{kg}.$ Calculate the velocity at which the shell leaves the gun.

A gun of mass ‘X’, fires a bullet of mass $25 \mathrm{g}$ with a velocity of $40 \mathrm{m}/\mathrm{s}$. Calculate the value of X, if the velocity of recoil of the gun is $0.5 \mathrm{m}/\mathrm{s}$.

A gun of mass$4.5 \mathrm{kg}$, fires a bullet of mass $20 \mathrm{g}$ with a velocity of $108 \mathrm{km}/\mathrm{hr}$. Calculate the velocity of recoil of the gun in SI system.

Water sprinkler used for grass lawns begins to rotate as soon as the water is supplied. Explain the principle on which it works.

Two friends on roller-skates are standing $5 \mathrm{m}$ apart, facing each other. One of them throws a ball of $2 \mathrm{kg}$ towards the other who catches it. How will this activity affect the position of the two? Explain your answer. 

Suppose a ball of mass $\mathrm{m}$ is thrown vertically upward with an initial speed $\mathrm{v}$, its speed decreases continuously till it becomes zero. Thereafter, the ball begins to fall downward and attains the speed $\mathrm{v}$ again before striking the ground. It implies that the magnitude of initial and final momentum of the ball is same. Yet, it is not an example of conservation of momentum. Explain why?

Two identical bullets are fired one by a light rifle and another by a heavy rifle with the same force. Which rifle will hurt the shoulder more and why?

Why are the road accidents at higher speeds more disastrous, as compared to those at low speeds? Explain.

How do the rockets operate in space? Explain.

Why do the tiny rockets used on festivals rise up, when ignited? Explain.

Why do the pieces of a cracker fall in all directions, when it is burst? Explain.
 

Why does an inflated balloon rise up vertically for some distance, when punctured from below? Explain.

 Why is it difficult to walk on marshy ground? Explain.
 

State the law of conservation of momentum.

Rocket works on the principle of conservation of:

An object of mass $1 \mathrm{kg}$ travelling in a straight line with a velocity of $10 \mathrm{m} {\mathrm{s}}^{-1}$collides and sticks to a stationary wooden block of mass $5 \mathrm{kg}$. Then, they move together in a straight line. The velocity of combined object is: