Q. A particle moves for 20 s with velocity $\ 3\ {ms}^{- 1}$ and then moves with velocity $4\ {ms}^{- 1}$ for another 20 s and finally moves with velocity $5\ {ms}^{- 1}$ for next 20 s. What is the average velocity of the particle?
A) $3\ {ms}^{- 1}$
B) $4\ {ms}^{- 1}$
C) $5\ {ms}^{- 1}$
D) Zero
Explanation
(b) Average velocity is that uniform velocity with which the object will cover the same displacement in same interval of time as it does with its actual variable velocity during that time interval.
Here, total distance covered
$\ \ \ \ \ \ \ \ \ \ = \left( 3\ {ms}^{- 1} \times 20\ s \right) + \left( 4\ {ms}^{- 1} \times 20\ s \right) + \left( 5\ ms^{- 1} \times 20\ s \right)$
$\ \ \ \ \ \ \ \ \ = (60 + 80 + 100) = 240\ m$
$Total\ time\ taken = 20 + 20 + 20 = 60\ s$
$\therefore Average\ velocity = \frac{240}{60} = 4\ ms^{- 1}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.