In Newtonian mechanics,which parameter is changed by the application of an external force?

$N$ number of balls,each of mass $m \ kg$,moving along the positive direction of the $x$-axis,strike a wall per second and return elastically. The velocity of each ball is $u \ m/s$. The force exerted on the wall by the balls in newtons is:

$A$ cricket ball of mass $250\, g$ collides with a bat with velocity $10\, m/s$ and returns with the same velocity within $0.01\, s$. The force exerted on the ball is ....... $N$.

$A$ ball of mass $0.5 \ kg$ is dropped from a height of $40 \ m$. The ball hits the ground and rises to a height of $10 \ m$. The impulse imparted to the ball during its collision with the ground is (Take $g = 9.8 \ m/s^2$)

$A$ ball of mass $150\,g$ starts moving with an acceleration of $20\,m/s^2$. When hit by a force,which acts on it for $0.1\,s$. The impulsive force is ........ $N-s$.

$A$ cricket ball of mass $500\, g$ collides with a bat with speed $15\, m/s$ and returns with the same speed within $0.01\, s$. The force acted on the bat is ............ $N$.