Question

✪ Physics question ✪

A body goes from P to Q with a velocity of 20 m/s and comes back from Q to P with a velocity of 30 m/s. Then the average velocity during the whole journey is : ​

Answer 1

Answer:

Average velocity =

Total time

Total displacement

Since, in this case, the particle initial and final points are the same, therefore its Displacement =0.

∴Average velocity=0

Answer 2

ANSWER:

• Average velocity = 0

GIVEN:

• A body goes from P to Q with a velocity of 20 m/s.

• Again comes back from Q to P with a velocity of 30 m/s.

TO FIND:

• The average velocity during the whole journey.

EXPLANATION:

$\boxed{ \bold{ \gray{ \large{Avg\ velocity = \dfrac{Total\ displacement}{Total\ time}}}}}$

Let displacement from P to Q be S and displacement from Q to P be - S.

Total displacement = S - S = 0

As displacement is zero, the average velocity will also be zero.

EXTRA CALCULATIONS:

$\boxed{ \bold{ \gray{ \large{Avg\ speed = \dfrac{Total\ distance}{Total\ time}}}}}$

Let distance from P to Q be S and distance from Q to P also be S.

Total distance = S + S = 2S

$\sf Total \ time = T_1 + T_2$

$\boxed{ \bold{ \gray{ \large{Time = \dfrac{Distance}{Speed}}}}}$

$\sf T_1 = \dfrac{S}{20}$

$\sf T_2= \dfrac{S}{30}$

$\sf Avg\ speed = \dfrac{S + S}{ \dfrac{S}{30} + \dfrac{S}{20}}$

$\sf Avg\ speed = \dfrac{2S}{ S \left(\dfrac{1}{30} + \dfrac{1}{20} \right)}$

$\sf Avg\ speed = \dfrac{2}{\dfrac{2 + 3}{60}}$

$\sf Avg\ speed = \dfrac{2}{\dfrac{5}{60}}$

$\sf Avg\ speed = \dfrac{2}{\dfrac{1}{12}}$

$\sf Avg\ speed = 2 \times 12$

$\sf Avg\ speed = 24 \ m {s}^{ - 1}$

Hence average speed = 24 m/s.