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## Passenger in a moving train

A passenger in a moving train tossed a coin which falls behind him .State the type of motion of the train ?

The train is in accelerated motion.

Explanation

If the train were moving with uniform velocity, the coin would fall back to the passenger’s hand (This is due to the inertia of motion of the coin. When it was thrown ‘vertically’ up, it had the same horizontal velocity as that of the train. Therefore, it will move alongwith the train and fall back to the thrower’s hand)

If the train is accelerated, the horizontal velocity of the train would be more than that of the coin (which remains constant through out its flight) by the time the coin returns. Therefore, the train travels a greater horizontal distance than the coin and the coin falls behind the passenger. ## Problem from Kinematics

The speed of a train changes from36km/h to 72km/h in 10sec. calculate the distance travelled during this time

u=36km/h = 10 m/s

v=72 km/h=20 m/s

t=10 s

S=?

use v = u+ at to find a

a = 1 m/s2

Use v2-u2=2aS to find S

S = (400-100)/2 = 150 m

## Numerical Problem from Laws of Motion

An 8000 kg engine pulls 40000 kg train alonged a level track and gives an acceleration of 1.2m/s2. Find the accelaration produced by same engine on a train of mass 16000kg?

Force exerted by the engine = mass of train x acceleration =  40000 x 1.2=48000N

When the same engine pulls a 16000 kg train, the acceleration = 48000/16000=3m/s2

## Pressure, area and railway tracks

Why the railway track are laid on large sized wooden or iron sleepers?

(SHARANYA  posted this question)

Trains have huge masses and rails are narrow. Therefore if they are directly put on earth, they will sink down due to the extreme pressure it would exert on earth when run over by the train. So they are laid on wooden or iron sleepers of large area so that pressure on earth is reduced.
Pressure = Force /Area.

As area increases pressure decreases.

## Centre of mass of an accelerated body

“What is the effect on centre of mass of system of particles when it is placed in accelerated train?” Vimal asked

## Path of an object

If a man tossed a coin in a moving train and the coin fell back . Then in which type of motion train is moving? and how?

CHANDRIMA

For the person who tosses the coin the motion is vertically upward if he do so. But for an observer outside the train the path of the stone is a parabola.This is due to the horizontal velocity of the stone.

If the stone fell back, it means that the train is accelerated. If it were moving with a constant velocity, then the stone would’ve reached back to his hands only as both the train and the stone possess the same horizontal velocity.

## Tossing a coin in a moving train.

if a man tossed a coin in a moving train and the coin fell back then in which type if motion train is moving? and how?

Answer: This shows that the train is accelerated. When the coin was thrown, it had the same velocity of the train. If the train was not accelerated, the coin would have fallen on to the hands of the man itself. But the accelerated train moves a greater horizontal distance than by the coin.

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