Question

an object starting from rest covers 20m in first 2 sec and 160m in next 4sec .what is its velocity after 7 sec?

Answer 1

Hi !

Initial velocity = u = 0m/s

Distance traveled = S = 20m
time  = t = 2 sec

Second equation of motion:-

S = ut + 1/2 at²

20= 0+ 1/2a x 2 ²

20 = 2a

a = 10 m/s²
========================
Velocity at the end of 2 sec:
v = u+at
   =  0+10*2
  = 20m/s

s = 160 m

160 = 20x 4+1/2(a1)4²

160 = 80+2a

8a1=80
a1 =10m/s²


hence , 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