An athlete runs for some distance before taking a long jump. Why?

$A$ force of $50\, dynes$ acts on a body of mass $5\, g$ which is at rest for an interval of $3\, seconds$. The impulse is:

$A$ particle of mass $m$ is moving with a uniform velocity $v_1$. It is given an impulse such that its velocity becomes $v_2$. The impulse is equal to

In an hour-glass,approximately $100$ grains of sand fall per second (starting from rest); and it takes $2 \, s$ for each sand particle to reach the bottom of the hour-glass. If the average mass of each sand particle is $0.2 \, g$,then the average force exerted by the falling sand on the bottom of the hour-glass is close to .......... $N$.

Which type of forces are responsible for the explosion of a chemical bomb: internal or external forces?

$A$ jet of water with cross-sectional area $A$ strikes a wall at an angle $\theta$ with the normal to the wall and rebounds elastically. If the density of water is $\rho$ and the velocity is $v$,what is the force exerted on the wall?