Question

4.A car travels the first third of a distance with a speed of 10 kmph, the second third at 20 kmph and the last third at 60 kmph. What is its mean speed over the entire distance?

Answer 1

Let the total distance traveled be s.
Hence the time taken for first third of the distance= t
1
​
=
v
1
​

s/3
​

Similarly, the time taken for second third of the distance= t
2
​
=
v
2
​

s/3
​

and the time taken for last third of the distance= t
3
​
=
v
3
​

s/3
​

Hence the mean speed over the distance=
t
1
​
+t
2
​
+t
3
​

s
​

=
v
1
​

1
​
+
v
2
​

1
​
+
v
3
​

1
​

3
​

=18km/h