If the coefficient of static friction between the tyres and road is $0.5$, what is the shortest distance in which an automobile can be stopped when travelling at $72\,km/h$?
Frictional force acting between road and lyres retards the motion of automobile. There is a static friction between tyres and road, so frictional force cause the retardation in velocity of a automobile. Free body diagram of automobile is shown. From Newton's third law
$F=f_{s}=\mu R=\mu g$ where $m$ is the mass of automobile. Also, $F=m a$ $m a=\mu m g$ $\Rightarrow a=$ retardation $=\mu\, g $ $=0.5\, g$ Let automobile stops at a distance $x$, then from equation of motion $v^{2} =u^{2}-2 a x$ Given, $v=0, u =72\, km / h =72 \times \frac{5}{18}\, m / s $ $=20 \,m / s $ $g =9.8 \,m / s ^{2}$ $\therefore 0^{2} =(20)^{2}-2 \times 0.5 \times 9.8 x$ $\Rightarrow x=\frac{20 \times 20}{2 \times 0.5 \times 9.8}=40.8\, m$
The laws of motion, which are the keystone of classical mechanics, are three statements that defined the relationships between the forces acting on a body and its motion. They were first disclosed by English physicist and mathematician Isaac Newton.
Newton’s First Law of Motion
Newton’s 1st law states that a body at rest or uniform motion will continue to be at rest or uniform motion until and unless a net external force acts on it.
Newton’s Second Law of Motion
Newton's 2nd law of motion deals with the relation between force and acceleration. According to the second law of motion, the acceleration of an object as built by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.
Newton’s Third Law of Motion
Newton's 3rd law of motion states when a body applies a force on another body that there is an equal and opposite reaction for every action.
