An object with a mass of $10\, kg$ moves at a constant velocity of $10\, m/s$. $A$ constant force then acts for $4\, s$ on the object and gives it a speed of $2\, m/s$ in the opposite direction. The force acting on the object is ......... $N$.

State Newton's second law of motion.

$A$ particle of mass $2/3 \, kg$ with velocity $v = -15 \, m/s$ at $t = -2 \, s$ is acted upon by a force $F = k - \beta t^2$. Here,$k = 8 \, N$ and $\beta = 2 \, N/s^2$. The motion is one-dimensional. Then,the speed at which the particle acceleration is zero again,is ........... $m/s$.

$A$ body of mass $10 \,kg$ is acted upon by a force given by the equation $F = (3t^2 - 30) \,N$. The initial velocity of the body is $10 \,m/s$. What is the velocity of the body after $5 \,s$ (in $\,m/s$)?

$A$ force of $100 \, dynes$ acts on a mass of $5 \, g$ for $10 \, s$. The velocity produced is ......... $cm/s$.

The magnitude and direction of the acceleration produced in a body of mass $5 \text{ kg}$ when two mutually perpendicular forces $8 \text{ N}$ and $6 \text{ N}$ act on it, are respectively: