Question

A car is moving with a uniform speed of $72km/h$. After applying brakes it stops after traveling $100m$ distance. If its mass along with the passengers is $1000kg$, then the value of force due to the application of brakes will be in newton:

Answer 1

Correct Answer: -2000

Explanation:
We know that,Force: The interaction which after applying on a body changes or try to change the state of rest or state of motion of the body is called force.Force $(F)=$ Mass $(m)\times$ acceleration (a)Retardation: The force acting in the opposite direction to the motion of a body is called the retarding force. This force produces negative acceleration for the body which is called retardation or deacceleration.Retardation $(a)=\frac{Force}{Mass}$The equation of motion is given below:$V=u+at$$V^2=u^2+2aS$Where $V$ is final velocity, $u$ is initial velocity, a is acceleration, $t$ is time and $S$ is distance.Given that:Mass $(m)=1000kg$Initial velocity $(u)=72km/h=\frac{(72\times 1000)}{3600}=20m/s$Distance $(S)=100m$Final velocity $(V)=0m/s$We know that car is stopped, which means the final velocity is 0.$V^2=u^2+2aS$$0={20}^2+2\times a\times 100$Acceleration $(a)=\frac{-400}{200}=-2m/s^2$Force $(F)=ma=1000\times (-2)=-2000N$Hence, the correct answer is $–2000$.

Answer 2

Newton's laws of motion are three fundamental classical mechanics rules that define the relationship between an object's motion and the forces acting on it. These laws are summarised as follows:

• Newton’s first law of motion: According to this law, everybody continues in its state of rest or uniform motion in a particular direction until and unless an external force is applied to change that state.
• Newton’s second law of motion: According to this law, When a body is acted upon by a force, the time rate of change of its momentum equals the force. i.e.

 F =  dp/dt = mdv/dt = ma

• Newton’s third law of motion:  According to this law, to every action, there is an equal and opposite reaction.

Equations of Motion

There are three equations of motion that only apply to uniformly accelerated motion. The following are the equations:

1. v = u + at
2. v² = u² + 2as
3. s = ut + 1/2 at²

Where

• u and v are the initial and final velocity of the particle
• t is the time taken 
• a is uniform acceleration
• s is the displacement of the body