Question

an object starts from rest travels 20m in the first 2sceconds and 160m in the next 4 seconds. what will be the velocity after 7 seconds from the start

Answer 1

the answer is.How I see this ;

At first -
u = 0 | v = ? |S = 20 | t = 2s | a = ?
S = ut + 1/2 at^2
=> 20 = 0 + 1/2 (a)(2)^2
=> (a)(2) = 20
Therefore at this instance a = 10m/s^2
And so v = u+at 
 v = 0 + (10)(2) = 20m/s

Secondly -
u = 20m/s |S = 160m | a = ? | v = ? | t = 4s
S = ut +1/2 at^2
=> 160 = 80 + 1/2 (a)(4)^2
=> 160 -80 = (8) (a)
=> 80 = (8)(a)
=> a = 10m/s^2
So now v = u +at
=> v = 20+ 40
=> v = 60m/s

Hope it will help you.