Question

An object starting from rest travels 20m in the first 2 sec. and 160 m in the next 4 sec. What will be velocity after 7 sec from the start?

Answer 1

Motion from O to A; u = 0, t = 2 sec, s = 20 m

Acceleration (a) = ?

s = ut + \(\frac{1}{2}\) at²

(Using the 2nd equation of motion)

⇒20 = 0 + \(\frac{1}{2}\) x a x (2)²

⇒ 2a = 20 

⇒ a = 10m/s²

Motion from O to B

u = 0, S = (20 + 160) = 180 m,

t = 2 + 4 = 6 sec, a = ?

Again,

s = ut + \(\frac{1}{2}\) at²

180 = 0 + \(\frac{1}{2}\) x a x (6)²

180 = 18a 

⇒ a = 10m/s²

This shows that body is moving with constant acceleration.

Motion from O to C,

u = 0, t = 7 sec, a = 10 m/s²  v = ?

v = u + at 

⇒ y = 0 + 10 x 7

⇒ v = 70 m/s