Question

3) A car travels a certain distance with a speed of 50 km/h & returns with a speed of 40 km/h. Calculate
(i) the average speed & (ii) average velocity of car for the whole journey.

Answer 1

Answer:

ANSWER

To complete 1km distance with speed =50kmhr it tkes time t

1

=

50

1

s

To complete 1km distance with speed =40kmhr it tkes time t

1

=

40

1

s

Average speed=

(1/50)+(1/40)

1+1

=44.44m/s

Answer 2

$\huge\mathfrak{Formula\:for\: average\:speed}$

• $Average speed$

$\Rightarrow\dfrac{total\:distance\:travelled}{total\:time\:taken}$

______________________________________

Given:—

$<strong>Speed = s_{1} = 50km/hr</strong>$

$<strong>Speed = s_{2} = 40km/hr</strong>$

$\text{let ,the total distance travelled be x.}$

$\text{From the distance ,we can find the time}$

$\text{taken of the two journeys}$

$\blue{\boxed{time = \dfrac{distance}{speed}}}</p><p>$

$<strong>S_</strong><strong>{</strong><strong>1</strong><strong>}</strong> \Rightarrow$$\blue{\boxed{time = \dfrac{x}{50}hr}}</p><p>$

$<strong>S</strong>_<strong>{</strong><strong>2</strong><strong>}</strong><strong> </strong>\Rightarrow$$\blue{\boxed{time = \dfrac{x}{40}hr}}$

$\red{\boxed{Average\:speed = \dfrac{x + x}{\dfrac{x}{50}+{\dfrac{x}{40}}}}}$

$\red{\boxed{Average\:speed = \dfrac{2x}{\dfrac{90x}{200}}}}$

$\red{\boxed{Average\:speed = \dfrac{2x}{90x} × 200}}$

$\red{\boxed{Average\:speed = \dfrac{40}{9}}}$

$\red{\boxed{Average\:speed = 4\dfrac{4}{9}km/hr}}$

$\text{(ii)Average velocity will be zero as displacement is zero.}$