Question

Question 58:
A boy walks from his classroom to the bookshop along a straight corridor towards North. He covers a distance of 20 m in 25 seconds to reach the bookshop. After buying a book, he travels the same distance in the same time to reach back in the classroom. Find (a) average speed, and (b) average velocity, of the boy.

Lakhmir Singh Physics Class 9

Answer 1

Given :

A boy walks from his classroom to the bookshop along a straight corridor towards North. He covers a distance of 20 m in 25 seconds to reach the bookshop

Distance from classroom to book shop =20m

time =25sec

After buying a book, he travels the same distance in the same time to reach back in the classroom

distance=20m
time=25 sec

I) Average speed = Total distance / Total Time
=(20+20)/(25+25)
=40/50
=0.8 m/s

II) Average Velocity= Displacement / Total time
 
As displacement is the shortest path between source and destination.
Here Displacement= 0  because child travels 20m forward and travels 20 m backwards .

Displacement=20-20=0

Hence Average velocity = 0/50 = 0m/s

Answer 2

Hello Dear,

Here is your answer,

Given Conditions---

(a) Distance between the Bookshop and the Classroom = 20 m.

A boys covered 20 m from the Classroom to the Book Shop and again came from  the Bookshop to the Classroom by covering the distance of 20 m.

Thus, Total Distance Covered by the Boy = 20 + 20
                                                                  = 40 m.

Total Time taken by the Boy = 25 + 25
                                             = 50 seconds.

Using the Formula,
 
 Average Speed = Total Distance/Total Time
                          = 40/50
                          = 0.8 m/s

Thus, the Average Speed of the Boy is 0.8 m/s.


(b) For Average Velocity,

Total Displacement Covered by the Boy = 0
[Since Boy returns to the Classroom, from where he had started his Journey.]

Total Time = 25 + 25
                 = 50 seconds.

Using the Formula,

   Average Velocity = Total Displacement/Total Time
                               = 0/50
                               = 0

Thus, the Average Velocity of the Boy is zero.


Hope it helps.