Question

An aeroplane land on a run way and comes to a stand still in 20 second when the brakeing force acting on wheels producing a retardgtion of 5 meter per second square find the initial velocity in kmper hour ​

Answer 1

Retardation = 5 m/sec^2

This means that:-

Acceleration =(-5)m/sec^2

$\rule{200}{2}$

Time taken to stop = 20seconds

The final velocity = 0m/sec

[As the Aeroplane is brought down to Rest]

$\rule{200}{2}$

From First Equation of Motion we have :-

$V=U+at\\ \\ \\U=V-at\\ \\ \\U=0-(-5)20\\ \\ \\U=0+100\\ \\ \\U=100m/sec$

$\rule{200}{2}$

Thus:-

The initial velocity of the plane was 100 m/sec

But :-

$1m/sec=\dfrac{18}{5}kmph$

so,

Initial velocity in Kmph will be :-

$=100*\dfrac{18}{5}\\ \\ \\=20*18\\ \\ \\=360\:Kmph$

$\rule{200}{2}$

Answer 2

MOTION :

Solution :

Since, Retardation is produced by applying the brakes , that means

Final velocity, v = 0 m/s

Time taken, t = 20 secs

Acceleration, a = - $\mathsf{5m{s}^{-2}}$

Using 1st equation of motion,

$\boxed{\mathsf{\green{v\:=\:u\:+\:at}}}$

$\mathsf{0\:=\:u\:+\:(-5)(20)}$

$\mathsf{u\:=\:100\:m{s}^{-1}}$

In kmph,

$\mathsf{u\:=\:{\dfrac{100*18}{5}}}$

⛛ $\boxed{\mathsf{\green{u\:=\:360\:km/hr}}}$