PSLV and GSLV are India’s popular satellites.

Two children $\mathrm{A}$ and $\mathrm{B}$ wearing skates face each other. $\mathrm{A}$ has a bag full of sand. He throws the bag towards $\mathrm{B}$. $\mathrm{B}$ catches it. What will you observe?

Conservation of linear momentum for a system is applicable only when the external forces acting on a system are zero.

A bullet of mass $20 \mathrm{g}$ is fired horizontally with a velocity of  $100 \mathrm{m} {\mathrm{s}}^{-1}$from a pistol of $1.5 \mathrm{kg}$. Calculate the recoil velocity of the pistol.

What do we mean by conservation of linear momentum? Under what conditions do we apply this concept?

External forces are the forces which act from outside the system.

The initial situation of two moving objects is shown in the figure. Suppose, after collision the two objects stick. What will be velocity of the two object system?

Conservation of linear momentum means that initial momentum is _____ (not equal / equal) to the final momentum.

A boy of mass $50 \mathrm{kg}$ running at $5 \mathrm{m} {\mathrm{s}}^{-1}$ jumps on to a trolley of $20 \mathrm{kg}$ travelling in the same direction at $1.5 \mathrm{m} {\mathrm{s}}^{-1}$. Find their common velocity.

What is conservation of linear momentum? Under what conditions can this concept be applied?

$$\begin{gathered} {\mathrm{m}}_1 = 60 \mathrm{kg} {\mathrm{m}}_2 = 50 \mathrm{kg} \\ {\mathrm{v}}_1= 5 \mathrm{m} {\mathrm{s}}^{-1} {\mathrm{v}}_2= 4 \mathrm{m} {\mathrm{s}}^{-1} \end{gathered}$$

Isolated systems of two skaters               Final velocity v = ? Both the skaters join hands

Suspend a good quality glass test tube containing some water by two strings on a stand as shown. Place a stop cork at the mouth of it. Start heating the test tube as shown below. What will you observe after some time?

Internal forces are the forces which bodies exert on each other when the bodies are a part of the system.

Isolated systems

Small fish is in the mouth of big fish. Find $\mathrm{v}$.