Question

an object starting from rest travels 20m in first 2 seconds and 160m in next 4 seconds what will be the velocity after 7 sec from the start?

Answer 1

Given:Initial velocity = u =0m/sDistance travelled =S=20mtime =t=2sec.From second equation of motion:S=ut + 1/2 at²20= 0*2+ 1/2a2²20=2aa=10m/s²velocity at the end of 2sec:V=u+at=0+10*2V=20m/sAfter 4sec, it covers a distance of 160mso,160=20*4+1/2(a¹)4²160=80+2a8a¹=80a¹=10m/s²It 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