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Question

An object starting from rest travels 20 m in first 2 seconds and 160 m in next 4 seconds. What will be the velocity after 7 seconds from the start?


Solution

Given:
Initial velocity = u =0m/s
Distance travelled =S=20m
time =t=2sec.
From second equation of motion:
S=ut + 1/2 at²
20= 0*2+ 1/2a2²
20=2a
a=10m/s²
velocity at the end of 2sec:
V=u+at
=0+10*2
V=20m/s
After 4sec, it covers a distance of 160m
so,
160=20*4+1/2(a¹)4²
160=80+2a
8a¹=80
a¹=10m/s²
It shows acceleration is uniform.
So, velocity at end of 7 sec from start:
V=u+at
= 0 + 10*7
=70m/s
∴the velocity after 7 sec from the start is 70m/s

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