Question

A car travels a certain distance with a
speed at 50 km/h and returns with a speed
al 40 km/h . Calculate (i) the average
speed and (ii), average velocity of car
for the whole journey​

Answer 1

Given:

Car travels certain distance with 50 km/hr and returns with a speed of 40 km/hr.

To find:

• Average Speed

• Average Velocity of car

Calculation:

Average speed be v avg.

$v \: avg. = \dfrac{total \: distance}{total \: time}$

$= > v \: avg. = \dfrac{s + s}{( \frac{s}{50} + \frac{s}{40} ) }$

$= > v \: avg. = \dfrac{2s}{( \frac{s}{50} + \frac{s}{40} ) }$

Cancelling s from numerator and denominator :

$= > v \: avg. = \dfrac{2}{( \frac{1}{50} + \frac{1}{40} ) }$

$= > v \: avg. = \dfrac{2}{( \frac{5 + 4}{200} ) }$

$= > v \: avg. = \dfrac{2 \times 200}{9}$

$= > v \: avg. = \dfrac{400}{9}$

$= > v \: avg. = 44.44 \: km {hr}^{ - 1}$

So average speed is 44.44 km/hr.

Let average velocity be u .

Totaldisplacement for the whole journey will be zero because the starting and the stopping. Of that object becomes same after a complete journey.

$u = \dfrac{total \: displacement}{total \: time}$

$= > u = \dfrac{0}{total \: time}$

$= > u = 0 \: km {hr}^{ - 1}$

So , average velocity will be zero.