Question

An object starting from rest covers 20 metres in first 2 seconds & 160 metres in next 4 seconds. What is its velocity after 7 seconds from the start?

Answer 1

Answer:

70 m/s

Explanation:

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

Finally -

u = 0 | t = 7s | a= 10m/s | v = ? | S = ?

v = u+at

=> v = 0 + (7)(10)

=> v = 70m/s