The rate of change of momentum is

State whether the following statement is true or false:
In any interaction,there are always at least two forces in play.

If a body experiences a net zero unbalanced force, then the body:

The quantitative definition of force is given by

What is momentum? Write its $SI$ unit. Interpret force in terms of momentum. Represent the following graphically:
$(a)$ Momentum versus velocity when mass is fixed.
$(b)$ Momentum versus mass when velocity is constant.

Explain the following:
$(i)$ Why do the doors of a corridor train open or shut when the train starts or stops?
$(ii)$ Why is it necessary to run along with a moving bus in the same direction while alighting from it?
$(iii)$ Why does a player run for some distance before taking a long jump?
$(iv)$ Why does a person fall off the back of a stationary horse if the horse starts off suddenly?
$(v)$ Why is a neat hole formed in a glass pane if a bullet is fired at it from a close range?