Question

7.
A train takes 2 h to reach station B from station A, and
then 3 h to return from station B to station A. The
distance between the two stations is 200 km. Find :
(i) the average speed, (ii) the average velocity of the
train.
Ans. (i) 80 km h-, (ii) zero.
​

Answer 1

Given :

Distance between station A & B = 200 km

time A to B, Tab = 2 h

time B to A, Tba = 3 h



Solution :

1.) For Average speed we know that

Avg Speed = total distance/ total time



so, total distance from A to B to A

= 2×200 km

= 400 km


total time = Tab + Tba = 2+3 = 5 h


so, average speed = 400/5 = 80 km/h


2.) For average velocity we know that

V avg = Total displacement / total time



as the train went from A to and returned back to A from B

so here the net displacement = 200 +(-200)

= 200-200 = 0 km

and total time = 2+3 = 5 h


so, V avg = 0km/ 5h = 0 km/h



Hence , for the journey

1. average speed = 80kmph

2. average velocity = Zero .

Answer 2

Answer:

$\implies$(1). Average speed => 80km/hr

$\implies$(2). Average velocity => 0. (zero)

$\large\underline\mathrm{Given:-}$

• Distance between the station A & B = 200km.
• Time A to B = 2hr
• Time B to A = 3hr

$\large\underline\mathrm{Solution}$

(1). The Average speed:

• Average speed = Total dist/Total time.

so, total dist from A to B to A.

$\implies$ 2 × 200km

$\implies$ 400km

Total time = T(AB) + T(BA)

$\implies$ 2 + 3

$\implies$ 5hr.

So, Average speed = 400/5

$\implies$ 80km/hr.

(2). The Average velocity:

• Average velocity = Total displacement/Total time.
• The train from A to and return back A from B.

So, the net displacement = 200 + (-200)

$\implies$ 200 - 200

$\implies$ 0

$\implies$ Total time = 2 + 3 $\implies$ 5hr

So, Average velocity => 0/5 => 0km/hr.

Hence, (1). Average speed => 80km/hr

(2). Average velocity => 0. (zero)