A particle moves for $20s$ with velocity $3m/s$ and then moves with velocity $4m/s$ for another $20s$ and finally moves with velocity $5m/s$ for next $20s$. what is the average velocity of the particle? (in m/s)

The correct option is C $4$

Distance=speed$x$ time

Distance rtaveled in first $20s$

$S_1=20s\times 3㎧$

$=60m$

Distance travelled in next $20s$

$S_2=20\times 4㎧$

$=80m$

Distance traveled in last $20s$

$S_3=20\times 5㎧$

$=100m$

Total distance traveled by particle

$S=S_1+S_2+S_3$

$=60+80+100$

$=240m$

Total time taken$t=20\times 3=60s$

$speed=\frac{distance}{time}$

$=\frac{240}{60}$

$\therefore V_{av}=4㎧$