Question

A car travels 30 km/ hr at a uniform speed of 40 km/hr. At the next 30 km at a uniform speed of 20 km/hr. Find its average speed.

Answer 1

Answer:

26.67 km/hrs.

Explanation:

Step by step explanation :

We know that,

Speed=Distance / time

.°. Time =dist / speed

Let's see the first case,

s = distance = 30 km

v = speed = 40 km/hr

t = time = 30 / 40

=3/4 hrs

Let's see the second case,

s = 30 km

v = 20 km/hr

t = 30 / 20

t = 3/2 hrs

Avg. Speed =Total distance/ Total time

=(30 + 30) / (3/4) + (3/2)

=60 / ( 3 + 6 ) /4

=60 / 9 × 4

=20 / 3 × 4

=80 / 3

=26.67 ( Approx. )

Hence,

Average speed of the car is 26.67 km/hrs ( Approx. )

Answer 2

Answer:

80/3 km/hr = 26.66

Explanation:

Given

• For 30 km car's speed remains 40 km/hr.

• for next 30 km it remains 20 km/hr.

To find

Average speed.

Formula for Average speed

$\sf \: \rightarrow \: avrg \: speed \: = \dfrac{total \: ditance}{total \: time}$

Procedure

We know,

$\rightarrow \sf \: speed = \dfrac{distance}{time}$

$\rightarrow \sf \: time = \dfrac{distance}{speed}$

$\rightarrow \sf \: time = \dfrac{30}{40}$

$\rightarrow \bf \: time = \dfrac{3}{4}$

$\rightarrow \sf \: speed\: {\footnotesize{2}}= \dfrac{d2}{t2}$

$\rightarrow \sf \: time \: {\footnotesize{2}}= \dfrac{d2}{s2}$

$\rightarrow \sf \: time \: {\footnotesize{2}}= \dfrac{30}{20}$

$\rightarrow \bf \: time \: {\footnotesize{2}}= \dfrac{3}{2}$

Total Time= T1 + T2

$\sf Total \: Time = \dfrac{3}{4} + \dfrac{3}{2}$

$Total \: Time \: = \dfrac{9}{4}$

$\sf \: \rightarrow \: avrg \: speed \: = \dfrac{total \: ditance}{total \: time}$

$\sf \: \rightarrow \: avrg \: speed \: = \dfrac{60km}{ \dfrac{9}{4} }$

$\sf \: \rightarrow \: avrg \: speed \: = \dfrac{60 \times 4}{9} = \dfrac{80}{3}$

= 26.66

What you need to make a note of ?

• Don't give away answer just in fractions , convert into decimal.

• Not only answer matters but steps too.

• Speed = Distance / time (most important equation)

• Average speed = Total distance/total time.

• Velocity is the speed of an object along a straight line (linear)