Question

An object starts from rest and travels 20m in the first 2s and 160m in the next 4s. Find its velocity at 7s after the start.

Answer 1

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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