Question

A superfast duronto express running at 90 kmph overtakes a bike running at 36 kmph in 25 seconds. What is the length of the train in meters?

Answer 1

Solution :-

Speed of Duronto express = 90 km/h

= 90 × 5/18

= 25 m/s

Speed of Bike = 36 km/h

= 36 × 5/18

= 10 m/s

Now relative speed of Train with respect to Bike

= 25 - 10

= 15 m/s

Now as time is 25 sec

=> Distance travelled by last compartment of train to overcome the bike .

= Relative speed × time

= 15 × 25

= 375 m

So length of train

$\Huge{\boxed{\sf{= 375 \: m }}}$

Answer 2

Actually welcome to the concept of mechanics.

Mechanics is the branch of physics which deals with the study of motion of material objects.

Mechanics can be further classified into the following :

• Statics : The branch of mechanics that deals with the study of object when it is at rest.

• Kinematics : The branch of mechanics that deals with the study of the object when it is in motion but without taking into account the factors.

• Dynamics : The branch of mechanics that deals with the study of the object when it is in motion taking into the account of the factors.

Coming to the Question :

Given:

Speed of Duronto Express = 90 km/h

Speed of Bike = 36 km/h

Also it is given that the express overtakes the bike in 25 seconds.

To Find :

The length of the train in metres.

Solution :

Converting the speeds of train and bike in m/s :

Speed of train = 90×5/18 = 25 m/s

Speed of bike = 36 × 5/18 = 10 m/s

So the relative speed = 25 -10 = 15 m/s

Then , the length of the train that overtook the bike :

Relative Speed × Time Taken

= 15 m/s × 25 s = 375 m

The required length of the train = 375 m

Relative Speed :

When objects 1 and 2 are moving with different speeds than the speed of one object 1 with respect to another object 2 is called relative speed of object 1 with respect to object 2.